Twelve lactatiug dairy cows were offered either fresh grass (G) or grass silage prepared from the same pasture which had undergone either an extensive (E) or restricted (R) fermentation, in a three-period change-over design experiment. Ensilage resulted in a reduction in forage pH and water-soluble carbohydrate concentration and an increase in ammonia-nitrogen concentration. The ensiling techniques used ensured that both silages were well preserved with pH values for E and R of 3.81 and 4.08 respectively, while the respective lactic acid concentrations were 124.6 and 27.0 g/kg dry matter respectively. Whilst there were no significant differences in dry-matter intake between treatments, when corrected for losses of volatile compounds, animals offered silage with a restricted fermentation consumed their food at a higher rate of intake (P < 0.001) than did animals on the other treatments. It was also found that while there was no significant difference in milk yield between animals offered fresh or ensiled forage, both butterfat and protein concentration and yields of butterfat were significantly higher (P < 0.01 or greater) with grass and restricted fermented silage than with extensively fermented silage. Ensiling of herbage had no significant effect on apparent digestibility. It is concluded that ensiling of herbage per se had little effect on overall animal performance but pattern of silage fermentation resulted in alterations in milk composition.

A study was carried out to examine the effects of ensiling and pattern of silage fermentation on nitrogen and energy utilization, rumen fermentation and rumen degradation characteristics of forage by lactating dairy cows. Six nonfistulated dairy cows and three rumen fistulated dairy cows were offered fresh grass (G) or grass silage produced from the same sward which had undergone either an extensive (E) or restricted (R) fermentation. Animals offered extensively fermented silage had liigher urinary nitrogen (N) outputs (expressed as a proportion of N intake) than those offered fresh grass (P < 0·05). Corresponding values for animals offered restricted fermented silage were intermediate between those offered grass and extensively fermented silage. Animals offered fresh grass and restricted fermented silage also had higher methane energy losses (P < 0·05), than those offered extensively fermented silage. The ensiling of grass had little effect on metabolizable energy (ME) intake or on the efficiency of utilization of ME for lactation (k1). Animals offered extensively fermented silage had higher proportions of propionate and lower proportions of acetate than those offered fresh grass or restricted fermented silage (P < 0·001). Ensiling resulted in an increase in the soluble (a) fraction and a reduction in the potentially degradable (b) fraction of N.

Forty pregnant F1 crossbred dairy cows (20 Friesian × Boran and 20 Simmental × Boran) were stratified in a 2 × 2 diet × work factorial experiment (not working-not supplemented, NWNS; not working-supplemented, NWS; working-not supplemented, WNS; and working-supplemented, WS). Working cows pulled sledges 100 days/year (pull = 350 to 450 N, 4 h/day, 4 days/week). Work output of supplemented and non-supplemented cows was similar over 1 and 2 years. Over all 3 years, dry-matter intake relative to metabolic body size (g/kg M0.75 was greater for working, compared with non-working cows. Body-weight changes and body condition score were similar for working and non-working cows. Non-supplemented cows lost weight throughout the first 2-year period, while supplemented cows tended to maintain or gain body weight over 1 and 3 years. Over 2 years, supplementation of working cows proportionately reduced live-weight loss by 0.73 and doubled the number of conceptions and parturitions. Days in milk, milk, milk fat and protein yields were similar for working and non-working cows, but were greater for supplemented, compared with non-supplemented, cows. Total conceptions and calves born in all 3 years tended to be greater for supplemented and non-working compared with non-supplemented and working cows. A productivity index (PI) that took into account food intake was calculated. The PI for supplemented cows over 2 years was greater than that for non-supplemented cows. Meanwhile the PI was similar for working and non-working cows over all periods considered. A similar PI for working and non-working cows under supplementation indicates potential of on-farm adoption of a cow traction technology that includes improved food production and ng strategies.

Forty pregnant F1 crossbred dairy cows (20 Friesian × Boran and 20 Simmental × Boran) were stratified in a 2 × 2 diet × work factorial arrangement (not working-not supplemented, NWNS; not working-supplemented, NWS; working-not supplemented, WNS; and working-supplemented, WS) were used to study the effect of work and diet supplementation on roughage intake, apparent digestibility of nutrients, digesta kinetics and plasma metabolites. Dry matter (DM) and organic matter (OM) intakes were greater for working than for non-working cows. Work and supplementation increased DM and OM in vivo apparent digestibility. This effect was particularly significant when comparing working cows at rest and at work. Passage rate and rumen mean retention of Cr-mordanted hay were similar for working and for nonworking cows. Liquid turn-over rate of Co-ethylene diamine tetra acetic acid (EDTA) was lower and rumen mean retention time of Co-EDTA was greater in working than in non-working cows whether supplemented or not. Working coios had lower plasma glucose during and immediately after working than non-working cows. Plasma non-esterified fatty acid (NEFA) was higher in working cows at the end of the working period and after rest between working hours. This effect was greater in non-supplemented than in supplemented cows. In working cows, β-hydroxybutyrate was lower at the end of working hours than in non-working cows. Lactate was greater in working than in non-working cows after the 3rd and 4th hours of work. Digesta kinetics could explain only partially the possible mechanisms responsible for greater roughage intake and apparent digestibility in working cows. The decrease of plasma glucose and the increase in NEFA during work indicates an increasing utilization of NEFA by muscle during consecutive working hours.

A nucleus dairy population using multiple ovulation and embryo transfer (MOET) was stochastically modelled with overlapping generations. The aim was to investigate the feasibility of controlling inbreeding in MOET breeding schemes using more realistic parameters for embryo recovery and best linear unbiased prediction (BLUP) for genetic evaluation. Four different cases (involving the culling of donors, more donors and the use of organized progeny testing of nucleus bulls) were studied in combination with nested and factorial designs. Further studies involved modifications of the selection index, including subtracting parental breeding values, inflating the genetic variance in the BLUP evaluation and penalizing inbred animals; these options were examined both with and without organized progeny testing. The effects of applying these schemes on both genetic response and rate of inbreeding were investigated. The results stressed the importance of incorporating progeny testing into MOET schemes for value of reducing inbreeding whilst maintaining genetic progress. There was no significant difference between nested and factorial designs. In the absence of progeny testing the inflation of genetic variance was more effective than subtracting parental breeding values at controlling inbreeding; however incorporating progeny testing made the latter strategy more potent and the superiority of inflating the genetic variance was in this case much smaller and non-significant.

Hierarchical (each dam mated to one sire) and factorial (each dam mated to several sires) designs involving juvenile selection in a closed nucleus breeding programme were compared for rates of genetic response and inbreeding using stochastic simulation. Numbers of sires and dams selected and herd sizes varied. Generations were discrete. Sires and dams were selected at 15 months on the basis of an estimated breeding value (EBV) calculated using selection index which considered information on close relatives. Selection was for total merit index. Matings were carried out assuming use of multiple emulation and embryo transfer (MOET) or in vitro embryo production (1VEP) technologies, over a range of reproductive parameters. Reproductive rates assumed a fixed number of potential offspring per collection with IVEP and MOET. Comparison of mating designs using MOET showed that rates of genetic response and inbreeding with factorial designs voere from 88 to 431% and 36 to 111% of those with the hierarchical design. Generally rates of genetic response were increased and inbreeding decreased by increasing the number of mates per dam due to a reduction of correlations among EBV. Reduced rates of genetic response were occasionally observed in factorial designs involving the mating of dams to large numbers of sires. This increased the generation interval due to the time to carry out the matings. Factorial designs were found to be most efficient for increasing genetic response and or decreasing inbreeding, for breeding programmes involving the selection of equal numbers of sires and dam. For the breeding programmes considered, rates of genetic response with IVEP equalled the best of the MOET designs, achieved at highest MOET rates, at the lowest level of IVEP. But at the equivalent rate of genetic response, rate of inbreeding was increased by 8%. The increased rate of inbreeding was due to the shorter generation interval with IVEP, and the increased probability of selecting related individuals assuming all donors respond to IVEP.

The effect of pregnancy on milk yield was studied on a 601 lactation sample. One hundred and sixty-nine lactations of non-pregnant cows, managed under identical conditions, served as controls. Lactations were divided into five groups according to parity (primiparous or multiparous) and production potential (two ranks for primiparous cows, three ranks for multiparous cows). The difference between the individual milk yield of each pregnant animal, and the mean production of the corresponding controls was computed weekly from the week of conception. The reducing effect of pregnancy began to be measurable from the 20th week of pregnancy, regardless of the group studied or the week of conception. Analysing the amplitude of this effect restricted the investigation to the three following groups: (i) primiparous cows, (ii) low- and medium-producing multiparous cows, (iii) high-producing multiparous cows. The effect of pregnancy was lower in primiparous than in multiparous cows. In the latter, it was higher in high-producing cows, partly because of the greater calf weight. At the 29th pregnancy week, this effect reached -17middot;5, -2·4 and -3·6 kg/day in the three groups, respectively. In each of these three lactation groups, the following non-linear model

Y = −e−a[(Pw~18)e−bpw]

was fitted, where Y is the difference between the milk yields of pregnant and non-pregnant cows at a given stage (week), Pw is the pregnancy week, and a and b are parameters. The overall milk yield losses over a complete lactation, as estimated from the integral of that equation, reached 89, 137 and 203 kg, respectively in the three groups.

Ardacin is an antibacterial glycopeptide with ruminal activity. The objective of this study was to measure its effects on food intake and growth rate of growing and finishing steers. Two experiments were carried out simultaneously using the same foods and the same ardacin supplementation levels. In experiment 1, 72 growing steers (8 months old and 240 kg initial weight) in four treatment groups were individually offered a basal diet of grass silage ad libitum. In experiment 2, 44 finishing steers (19 months old and 463 kg initial weight), also in four treatment groups were individually offered a basal diet of grass silage ad libitum plus 3 kg (5 kg for the final 28 days) concentrates per head daily. The four treatments were 0, 50, 125 and 210 mg ardacin per head daily incorporated into 1 kg ground barley. This was offered in addition to the basal diet. The duration of the experimental period was 154 days after which 48 of the growing steers were put to pasture for a 196-day grazing season. The finishing steers were slaughtered following a withdrawal period of 7 days. Mean daily silage dry-matter intakes, and mean daily total metabolizable energy intakes for the treatments as listed above were 4·91, 5·15, 5·10 and 5·03 (s.e. 0·083) kg and 63, 66, 65 and 65 (s.e. 0·7) MJ (experiment 1), and 5·63, 5·62, 5·51 and 5·54 (s.e. 0·059) kg and 108, 108, 107 and 107 (s.e. 0·4) MJ (experiment 2), respectively. In the same order, mean daily live-weight gains during the treatment period were 612, 758, 784 and 798 (s.e. 25·2) g (experiment 1) and 911, 942, 851 and 860 (s.e. 40·0) g (experiment 2). In the growing steers proportionately 0·64 of the weight response to ardacin was retained to the end of the following grazing season. It is concluded that ardacin supplementation increased live-weight gain and improved the efficiency of conversion of food to live weight in growing steers but had no significant effect on finishing steers in this study.

Friesian steer cahes were reared over winter on a silage (S) or on a silage plus concentrate (SC) diet to provide cattle of the same live weight, but of different ages for a comparison of grazing and feeding cut herbage indoors during the summer. A further group received fish meal (SF) as a supplement in an attempt to provide cattle of the same age as the S group, but of different body composition. Although supplementation improved the daily deposition of fat and protein, it did not lead to differences in body composition at the end of the winter period. The ratio of protein to fat deposition and the efficiencies of conversion were low for all groups, but they did improve as the level of supplementation increased.

There was no carry-over effect of winter treatment on summer performance. However, housed cattle deposited significantly more fat.

The trial demonstrated the inefficient use of nitrogen from silage with poor fermentation characteristics and the predisposition of cattle on such diets to low protein to energy retention. Whilst supplementation altered this balance, higher levels than given would be needed to have a marked effect. It was also concluded that the performance of housed cattle as an indicator of that of grazing cattle, is likely to be misleading because lower activity reduces maintenance requirement and leads to greater fat deposition.

A study was carried out to examine the effects of method of grass conservation on intake and apparent digestibility by sheep and rate of degradation in the rumen of cattle. Thirty-six hoggets were arranged in a three-period partial change-over design involving nine treatments. The treatments consisted of fresh herbage or herbage from the same pasture which was ensiled for 2, 4, 7, 10, 20 and 41 days in round bales or herbage from the same pasture conserved as hay or ensiled in a bunker silo for 51 days. In addition the rate of dry-matter disappearance in the rumen for each treatment was determined using three rumen fistulated steers. The fresh and ensiled treatments had been frozen prior to feeding. Results from the study showed that the dry-matter intakes, corrected for losses of volatile compounds, of material ensiled in round bales, was increasingly depressed with period of ensiling up to 20 days after ensiling. Intakes of digestible energy followed a similar trend. Regression analysis indicated that reductions in intake with ensiling were mainly due to increases in ammonia N and n-butyric acid concentration, while changes in pH, water-soluble carbohydrate and acetic acid concentration also influenced intake. The differences in intakes of dry matter and digestible energy between fresh herbage and herbage from the bunker silo were not significant. The ensiling of herbage in round bales had little effect on organic matter apparent digestibility but led to an increase in nitrogen apparent digestibility and effective degradability when calculated at rumen outflow rates of 0·05 per h and 0·08 per h. Conservation of grass as hay led to a reduction in the intake, apparent digestibility and effective degradability of dry matter.

A study urns conducted to determine the best method of preparation of silage and freshly cut forage samples for the estimation of rumen degradability by the nylon bag technique. Three types of forage were evaluated: a grass silage, a fresh grass (ryegrass) and a fresh legume (white clover). For each forage, six preparation methods were compared: chopping fresh (FRS); chopping and macerating fresh (FMC); chopping, freezing, thawing and macerating (FRZ); freeze-drying (FD); low-temperature oven-drying (45°C, 72 h) (OVD); high-temperature oven-drying (160°C, 90 min) (DHD). Dried samples were hammer-milled (2·5-mm screen). Chemical composition and rumen degradability were affected by the method of preparation. Protein fractions were sensitive to drying method, and oven-drying reduced nitrogen (N) solubility and degradability as the severity of the heating was increased. OVD and DHD gave lower estimates of N and dry matter (DM) solubility and degradability than FD. The effect of drying method on DM degradability was to reduce solubility and effective degradability, calculated for an outflow rate of 0·033 per h, but not potential degradability.

Silage DM degradability was less affected than that of fresh forages. Freshly prepared samples (FRS, FMC, FRZ) gave lower estimates of N and DM solubility and degradability than FD, the differences being least with silage and FRZ, which was the most effective at rupturing plant structures of the FRS, FMC and FRZ methods. Of the six preparation methods, freeze-drying was the most effective preparation method. FRZ and OVD were less effective, but similar to each other. The small particles (calculated) produced by grinding dried samples may result in an overestimation of zero time losses and hence the degradability of the sample. These undesirable effects might be minimized by coarser grinding (4-mm screen) and correction for particulate matter loss.

The cover comb has been developed in New Zealand as a means of increasing residual fleece depth after shearing and so increasing the resistance of shorn sheep to cold stress.

The effects of shearing by cover comb and standard comb were studied over 2 days pre-shearing and 10 days post-shearing in eight pairs of non-pregnant, non-lactating 2-year-old ewes. Animals were housed and given a maintenance level of chaffed lucerne hay. One member of each pair was shorn with a cover comb, the other with a standard comb. Each pair was exposed to ‘cold plus wind’ (7°C ambient temperature, 7 km/h air movement) followed by ‘cold plus wind plus rain’ (10°C ambient temperature, 7km/h air movement, wetting at a rate equivalent to 25 mm/h rain from overhead sprinklers) in a calorimetry chamber on days S –3, S –2, SO (day of shearing), S2, S6 and S10. Heat production immediately after shearing (SO) was proportionately 0·22 greater in ewes shorn by the standard comb under conditions of ‘cold plus wind’ and 0·38 greater under conditions of ‘cold plus wind plus rain’ than in their cover comb-shorn cohorts. Circulating concentrations of non-esterifiedfatty acids were substantially elevated on the day of shearing and 2 days thereafter in ewes shorn by the standard comb, indicating increased rates of body fat mobilization to support heat production in these ewes compared with those shorn by the cover comb. This was reflected in a 1·4 kg weight loss in the standard comb-shorn ewes compared with a 0·4 kg live-weight gain in the cover comb-shorn group over the 10 days of the experiment. It was concluded that use of a cover comb will significantly reduce the risk of death from hypothermia in sheep shorn during winter and spring, and should facilitate an increase in the productivity of animals by allowing a greater proportion of food energy to be used for productive purposes.

A selection index for overall economic merit and five subindexes for maternal and lamb traits were constructed. For estimation of breeding values, two computer programs were developed. A multiple-trait animal model was programmed for the ewe traits including number of lambs born ofl-, 2- and 3-years-old ewes and ewe fleece weight of yearlings. In order to reduce the memory requirement, the lamb data (growth rate, carcass weight, carcass grade, fat% and lamb fleece iveight) were analysed by a reduced multiple-trait animal model including genetic maternal effect. Experiences with the computer programs in genetic evaluation of approximately 619 000 animals are presented. It is concluded that the models and computing strategy may be used for genetic evaluation in the national sheep breeding programme in Norway.

Relative economic values for all traits were derived from a profit equation on a 3-year-old ewe basis. The sensitivity towards changed economic values urns found to be low. Further, the genetic change in the ewe traits of the Norwegian breeds has been estimated, and a significant improvement was found, which was two to four times higher in the ram circles than outside. For breeding rams, the genetic change for number of lambs born was estimated to be approximately 0·01 lambs per ewe and year.

Uterine capacity was estimated in Chinese Meishan (MS), Large White (LW) and crossbred (LW × MS) sows, using unilateral liysterectomy-ovariectomy (UHO) methods. In the first two parities, 20 sows of each genotype, whose left uterine horn and ovary had been removed in the post-pubertal period, were mated, their ovulation rate recorded by laparoscopy and allowed to farrow normally. In the third parity the mated sows were slaughtered at around 30 days of pregnancy and ovarian, uterine and embryo traits were recorded. The ovulation rate in UHO females was similar to that observed previously in intact females of the same population, MS sows producing 4·2 (s.e. 1·0) more ova at parities 1 and 2 and 7·0 (s.e. 1·9) more ova at parity 3 than LW sows. At parity 3, MS sows had 5·9 (s.e. 2·0) more viable embryos at 30 days of pregnancy than LW sows. Crossbred sows were intermediate for both ovulation rate and the number of viable embryos at 30 days. At the first two parities, litter size was higher in the MS by 1·0 (s.e. 0·8) piglets per litter than in the LW, while the crossbred sows exceeded the mid-breed mean by 1·7 (s.e. 0·7) piglets. Uterine capacity, estimated as twice the number of piglets carried to term in a single horn, was 12 foetuses in the LW, 14 in the MS and 16 in the crossbred sow. Piglets born to MS sows were 0·4 (s.e. 0·1) kg lighter than those born to LW sows, with a significantly lower (MS: LW = 0-68, P < 0·01) within-Utter standard deviation, which was found to be independent of the smaller mean weight. At parity 3, MS sows were found to have uteri of similar length with both lighter (-0·36 (s.e. 0·14) g) and shorter (-1·54 (s.e. 0·76) mm) embryos with smaller spaces (-7·8 (s.e. 2·7) cm) between embryo sites than LW sows. Within-Utter standard deviations for embryo size traits were lower in MS than in LW sows, especially for the distance between embryo sites (MS: LW = 0·45, P<0·01). The reduced variability of embryo traits in litters in MS sows was independent of their smaller litter means. Third parity litters from crossbred sows were similar to the mid-breed mean for means and variability of embryo traits but crossbred sows had significantly longer uteri (48·5 (s.e. 18·5) cm) than the mid-breed mean, being longer than either pure breed. It was concluded that differences between the pure breeds in uterine capacity may have arisen through better within-uterus organization, whereas the observed heterosis effects may result in part from physically longer uteri in crossbred sows and that uterine capacity contributes to the genotype differences in prenatal survival and prolificacy, especially in crossbred sows.

Fifty-four multiparous Yorkshire × Landrace sows were allocated equally to receive an intramuscular (i.m.) injection of 3 ing oestradiol-17β (E2) or no injection at 112 days of gestationto determine the effect of E2 on the timing and duration offarrowing. All sows received an injection (i.m.) of 10 mg prostaglandin F2x af 113 days of gestation. Of the soivs allocated to treatment, 21 oestrogen-treated and 19 control sows were assigned to be observed for the onset of parturition. A further six oestrogen-treated and eight control sows were included to increase the data base for litter production. The time of piglet delivery was monitored between 08·00 and 18·00 h on day 114 of gestation. Blood samples were obtained from each offour piglets from four E2-treated and five control litters. More E2-treated (8/21) than control sows (1/19) farrowed before 08.00 h of day 114 (P < 0·05) although, for those sows farrowing during the observation period, there was no effect on the time to onset or duration of parturition. Plasma oestradiol concentrations were higher (P < 0·06) in piglets delivered by E2-treated sows. However,this was not associated with any effect on piglet pre-weaning survival. It is concluded that exogenous oestradiol can influence the timing of onset offarrowing in some sows. Although further refinement in terms of timing of E2 injections is required, it seems likely that exogenous E2 may have a useful role to play in hastening the induction of parturition in sows.

One of the more promising techniques for the improvement of sow productivity has been the use of partial weaning or the separation of the sow and litter for periods of between 3 to 12 h/day towards the end of lactation. The purpose of the present study was to examine changes in steroid hormone concentrations, oestrus and fertility responses in lactating sows subjected to altered sucking, boar exposure and gonadotropins in mid lactation and at weaning. Thirty-two crossbred sows were allocated at random to one of four experimental treatments. Treatment 1 sows (no. = 8) were separated from their respective litters for 3 h/day from 12 days post partum through until weaning which was carried out at 21 days post partum. Treatment 1 sows were also given in-pen boar exposure for 1 h/day between day 12 post partum and weaning. Treatment 2 sows (no. = 8) were given the same protocol of litter separation (LS) and boar exposure (BE) as in treatment 1 and they were also given a combination of gonadotropins (Gn) on day 17 of lactation. Treatment 3 sows (no. = 8) were given LS + BE as above and the sows were injected with Gn on the day of weaning. Treatment 4 sows were controls given no LS, BE or Gn (no. = 8). During lactation, treatment 1 sows exhibited significantly (P < 0·05) reduced progesterone concentrations compared with treatment 2 sows. There were no other significant effects of treatment for any of the periods considered. The separation of sows from their piglets with or without gonadotropic treatment did not result in lactational oestrus in any treated sows. No significant treatment differences were found in the subsequent litter size (piglets born alive or total number of piglets). In conclusion, the present results have demonstrated no significant effects of LS, BE and Gn treatment during lactation on sow and litter performance. This was associated with low levels of peripheral plasma progesterone in all lactating sows.

Forty-eight 4-week-old White Rock growing chickens (mean live weight 500 (s.e. 9·3) g) were given, by crop intubation, four isoencrgetic (13·1 M] metabolizable energy (ME) per kg dry matter (DM)) and isonitrogenous (120 g crude protein (CP) per kg DM) semisynthetic diets based on vetch (V) or bitter vetch (B) seeds, untreated or antoclaved at 120°C for 30 ruin (diets V, AV, B and AB, respectively). Autoclaving of the seeds caused some changes in amino acid (AA) composition but did not reduce the availability of A As, especially of lysine.

The average apparent AA digestibility values derived from ileal content were 0·75, 0·85, 0·59 and 0·85 for diets V, AV, B and AB, respectively, corresponding to true absorption values of 0·90, 1·00, 0·74 and 0·97, respectively. Although the apparent digestibility values of several AAs were relatively low (methionine, isoleucine, tyrosine and cystine), most were higher than 0·70. Heat treatment resulted in a significant increase (P < 0·05) in the AA apparent digestibility of both seeds. It is concluded that heat treatment is useful for improvement of vetch and bitter vetch seeds for inclusion in poultry diets.

Although the extent of ossification between the caracoid and clavicle bones of the pectoral girdle (ossa cinguli membrii thoracici) in the ostrich carcass can be used to determine between ossification classes within the age range 8 to 14 months (considered as the optimal time of slaughter of ostriches), it is not an accurate tool for estimating the exact age at slaughter. It is possible to distinguish between carcasses originating from the birds between 10 and 12 months of age, at which ostrich meat toughens.

The possible influence of social factors on the timing of puberty in the hind was investigated utilizing seasonally advanced (melatonin-treated) hinds and stags. Melatonin treatment of both sexes resulted in a significant advancement in the onset of pubertal ovarian activity (26 days, P < 0·001) and calving (27 days, P < 0·001) in the treated hinds and antler casting (25 days, P < 0·001) in the treated stags. Ovarian activity and calving were not influenced by melatonin treatment of the stags alone and similarly, antler casting was not affected by melatonin treatment of the hinds alone. However, a group of hinds without stags until after the onset of the breeding season, reached puberty later (5 days, P < 0·05) than hinds with stags, suggesting the presence of the male is important in determining the timing of puberty.