An analysis is undertaken of the effect of errors in estimates of parameters on the response to selection for an economically important trait (trait 1) when one or more additional traits are added in a selection index. The detailed analysis is confined to one additional trait (trait 2) which contributes useful information unless the genetic and phenotypic regressions of trait 1 on trait 2 are equal.

If there are errors in parameter estimates the extra response obtained by including trait 2 will usually be over-predicted. When trait 2 actually contributes no useful information the predicted benefit equals the real loss in efficiency from its inclusion.

The loss in efficiency from poor estimation of parameters, whether or not the second trait makes a contribution, is roughly one-quarter of the squared coefficient of variation of a heritability estimate of trait 1 in the same experiment.

The relationship between two methods of sire evaluation (Bar-Anan and Sacks's cumulative difference method (CD) and Henderson's best linear unbiased predictor method (BLUP)) is shown. This relationship suggests a modification, with more theoretical justification, to the CD method.

Dissection data from 643 carcasses of castrated male cattle (steers) of 15 breed-type × feeding system groups were used to examine the distribution of total fat (TF) between subcutaneous (SF), intermuscular (IF), kidney knob and channel (KKCF) and cod fat depots. The breed-type groups, which were from cereal or grass/cereal feeding systems, included Ayrshire, Simmental × Ayrshire, British Friesian and Friesian crosses with Aberdeen Angus, Hereford, Limousin, Charolais, South Devon and Simmental. Means for percentage TF in side ranged from 21·4 to 36·2 with a pooled within group SD of 3·87.

The growth of each depot relative to TF was examined using the allometric equation. Significant but not large differences existed between groups for the growth coefficients of SF and IF while the coefficients for KKCF differed widely among groups. The coefficient for SF was greater than that for IF in every group (pooled within-group b values±SE were 1·20±·02 and 0·87±0·01 respectively).

At constant TF weight, carcasses from Ayrshire and Ayrshire crosses tended to contain less SF and more IF+KKC F than those from Friesian and beef breed × Friesian. Important differences in distribution were recorded between the various beef breed × Friesian groups. The proportion of SF was lower for cattle fed on grass/cereal diets than for cattle of the same breed type fed on cereal diets.

The differences in fat distribution led to substantial bias for some groups when the percentages of IF and TF in the side were predicted from percentage SF. The bias was less when both KKCF and SF were used as predictors.

1. Two series of energy balance trials were conducted with British Friesian veal calves. In the first, calves were given a milk replacer diet at three different planes of nutrition. In the second, calves were raised from about 80 to 180 kg at four air temperatures, 5°, 10°, 15° and 20°.

2. The net efficiency of utilization of the milk replacer diet for growth was 0·72. The effect of body size on heat production in growing calves was best expressed by an exponent of body weight slightly but not significantly below W0·75.

3. Measurements of heat production estimated from respiratory exchange and heat loss measured by direct calorimetry agreed exactly at all planes of nutrition. Heat production at zero energy retention was 675 kJ/kg W0·75 per 24 hr.

4. Average daily live-weight gain and total heat loss were the same at all air temperatures. Changes during growth in the partition of heat loss into its sensible and evaporative components indicated that calves acclimated progressively to the air temperatures to which they were exposed.

1. Eight British Friesian and eight Jersey calves were fed fresh milk during the period from 3 days to 40 days of age, at two levels of feeding.

2. Energy and nitrogen balances were measured twice for each calf.

3. Fasting heat production (FHP) (MJ/day), which was measured on these occasions, was related to live weight (kg) by FHP = 0·435 W0·75. There was no significant difference in FHP/kg0·75 between the breeds but previous level of feeding and the duration of fast had significant effects.

4. The data for heat production, metabolizable energy (ME) intake and energy retention were interpreted to provide estimates of ‘true’ net energy required for maintenance of 0·23–0·27 MJ/kg0·75 daily.

5. Pooled values for ME required for maintenance and for the net efficiency of utilization of ME above maintenance were 0·39 or 0·42 MJ ME/kg0·75 daily, and 0·67 or 0·72 determined by simple or multiple regression techniques respectively; there were no significant differences between the breeds. Pooled values for the partial net efficiencies of utilization of ME for the synthesis of protein and fat were 0·54 and 0·79 respectively.

6. ME required above maintenance was estimated to be 11·3 and 13·6 MJ ME/kg of live-weight gain for the lower and higher rates of gain respectively.

7. A small experiment revealed no major differences between diets of milk alone or milk plus solid food, with regard to maintenance requirement or net efficiency of utilization of ME by calves.

Components of reproductive efficiency of Zebu-type and Charolais × Zebu-type (1/2, 3/4 and 7/8) females were compared. Zebus had longer mean intervals from calving to first service (57·8 days) and from calving to conception (46·0 days). Least squares means for both traits were respectively 129·8 and 145·1 days. Correspondingly, in the Charolais cross group 26·4% more cows were detected in oestrus within 180 days of calving, and 31·4% more conceived in the same period. Least squares means for these traits were respectively 80·7 and 50·5%.

No significant differences were found between the two breeding types either in number of services per conception or in the percentage conceiving by artificial insemination (of those showing oestrus) both for lactating and dry females. A higher percentage of oestrus cycles of normal duration was found in Charolais cross (72·9 %) than in Zebus (63·1%). Gestation lengths of Zebus (Indu-Brasil sires) and Charolais cross (Charolais and Simmental sires) were respectively 288·8 and 283·1 days.

The main difference between breed types was the longer lactation anoestrus shown by Zebus. These were very sensitive to seasonal effects, showing a cyclical time trend with peaks of shorter anoestrous periods for cows calving in January–February–March, and longer ones for cows calving in July–August–September. Related traits followed parallel cycles. Charolais cross cows showed less variation than Zebus.

New methods of design and analysis for mixed grazing experiments are proposed and compared with previously reported designs. In general, with previous designs the effects of mixed grazing per se were confounded with other factors. The concepts of equality of grazing pressure and of livestock equivalents are examined and criticized when used as starting points for mixed grazing experiments. Two year's results of a mixed grazing experiment with cattle and sheep are analysed and provide evidence that mixed grazing is beneficial to both species in terms of production per animal. A simple economic analysis shows how the price ratio between the value per unit weight gain of the two species can be used to decide on the area of financial benefit from mixed- as opposed to single-species enterprises.

Measurements of the live weight and body condition of 105 Scottish Blackface, North Country Cheviot and South Country Cheviot male sheep (rams) per year were made at three locations over a period of 2 years.

A distinct cyclical pattern of change in live weight and body condition throughout the year was apparent in all rams. Maximum values recorded in the autumn were followed by rapid and substantial losses throughout the mating period, with recovery of both weight and condition during the spring and summer months. The amplitude of the annual live-weight curve was of the order of 20 kg (22%) and that of body condition was more than 1 unit.

The patterns of annual change in live weight and of inferred change in body composition of rams are compared with those of ewes, and some of the probable effects on production are considered.

Incubation with rumen liquor gave a lower rate of release of ammonia and a higher dehydrogenase activity with urea phosphate (UP) than with urea.

Four concentrate diets containing 13 % crude protein, 27% of which was supplied by urea or three different forms of UP, were each given to eight Awassi lambs. With twice-daily feeding (but not five-times daily feeding), a beneficial effect of UP over urea was observed, expressed in lower blood ammonia and urea levels. There was no effect on the pH of rumen liquor.

In a N-balance experiment with 24 lambs, four diets were examined: a basal diet containing 9·5% crude protein and three other diets in which the crude protein content was raised to 13% by addition of soya bean meal, urea or UP. The diets were given twice daily. Urea phosphate and the soya bean meal gave a significant increase in N retention whereas the urea treatment did not. However, the difference in N retention between the UP and urea treatments was not significant. Total volatile fatty acid concentrations in the rumen did not differ significantly between treatments but the ratio of acetic to propionic acids was significantly lower with the urea diet.

Ten Landrace × (Landrace × Large White) young female pigs (gilts) were allocated to each of three growth rate treatments so that they attained 73 kg live weight at 135, 160 or 190 days of age. At 73 kg live weight the gilts were introduced to a vasectomized boar for 30 min each day, and were subsequently mated at the second oestrous period. The interval from boar introduction to puberty was 15·2 and 19·0 days respectively for gilts having first boar contact at 190 and 160 days of age, these intervals being significantly shorter (P<0·05) than the 34·3 days for the 135-day group. However, the mean ages at puberty of the 135- and 160-day groups (169·4 and 178·2 days respectively) were not significantly different but these gilts were significantly younger at puberty than the 190-day group (205·3 days). There were no significant differences between treatments for gilt live weight at puberty or first litter size.

Two castrated male pigs from each of 620 litters were fed ad libitum to 90 kg market weight at three stations. The pigs represented 20 three-breed crosses produced by mating Yorkshire, Landrace, Lacombe, Hampshire and Duroc sires to Landrace-Yorkshire, Hampshire-Landrace, Large Black-Lacombe, Large Black-Landrace, Duroc-Lacombe and Duroc-Yorkshire dams. The data on feed conversion, average daily gain, age at slaughter, backfat thickness and area of loin eye muscle were analysed by least-squares.

Within breed cross of dam, pigs sired by Hampshire were consistently superior in feed conversion, carcass quality and in 3 crosses out of 5 had the fastest growth rate during the fattening period. They were, however, the oldest at 90 kg live weight. Pigs sired by Duroc ranked second in carcass quality and growth rate, whereas those sired by Landrace had the slowest growth rate. The pigs produced by Hampshire-Landrace sows were superior in carcass quality but inferior in feed conversion and growth to those from sows of the other five crosses.

In descending order, the four highest ranking crosses based on an index combining average daily gain, backfat thickness and feed efficiency were Hampshire × (Landrace-Yorkshire), Hampshire × (Duroc-Lacombe), Duroc × (Landrace-Yorkshire) and Hampshire × (Large Black-Landrace).

Animal Production, Volume 20, part 2, pp. 249–255

Evaluation of crossbred sows for the production of pigs for slaughter

M. H. Fahmy, W. B. Holtmann and T. M. Macintyre

In Table 3, some of the rankings shown in parentheses are erroneous. The rankings shown should be ignored and recalculated from the breed mean values.

A total of 177 sows representing five two-breed crosses were used in a 2×2 factorial experiment to study the effects of post-weaning stress (changing environment and group housing) and feeding regime (flushing by feeding ad libitum until mating) on the weaning-oestrus interval and other reproductive traits up to 30 days of pregnancy.

The group which was stressed had about 10% (P<0·05) fewer reproductive failures than those not stressed, while little difference was found between the two feeding regimes. About 61% of the flushed sows returned to oestrus within 7 days after weaning, 9% higher than for those not flushed. The stress treatment had little effect on the weaning-oestrus interval. Neither treatment affected ovarian and follicular-fluid weights, percentage of follicles of different sizes, ovulation rate nor number of viable embryos. The flushed group, however, had 9% lower embryo survival than the group not flushed. A positive relation was found between the number of days on ad libitum feeding and ovulation rate and embryonic mortality.

Differences among breeds were significant for all the traits, except weaning-oestrus interval, weight of follicular fluids, percentage of large follicles, ovulation and survival rates. The weaning-oestrus interval was not significantly correlated with any of the reproductive traits studied.

1. Three pigs prepared with re-entrant cannulae in the proximal duodenum and terminal ileum were used to study flow rate of nitrogen, and digestion and absorption of dry matter, nitrogen, gross energy and starch. The pigs were given a semi-purified diet, a hard wheat diet and a soft wheat diet. These were approximately isonitrogenous.

2. Nitrogen content of insoluble dry matter of duodenal digesta was much higher on the semi-purified diet than on the wheat-based diets.

3. Apparent digestibilities of dry matter, energy and nitrogen in the small intestine were in the order semi-purified diet > hard wheat > soft wheat although differences were not statistically significant. Similar results were obtained for total digestibility of these components.

4. Absorption of most amino acids from the small intestine was higher for casein in the semi-purified diet than for wheat protein. Significantly more lysine, arginine, isoleucine and tyrosine were absorbed from hard than from soft wheat.

5. With all diets there was almost complete digestion of starch in the small intestine.

6. There was little digestion of nutrients in the large intestine, and thus digestibilities calculated from faecal analyses showed similar trends to those calculated from analyses of digesta from the terminal ileum. Most values compared favourably with those reported elsewhere for digestibilities of amino acids in wheat.

7. It was concluded that casein was superior to the wheat proteins but that protein of hard wheat was of better quality than that of soft wheat when evaluated by ileal recovery of animo acids, due largely to a greater absorption of lysine.

Several of the various dairy sire evaluation methods now in use account for the genetic level of contemporary herdmates. In the cumulative difference method of Bar-Anan and Sacks the contemporary comparison estimate is first calculated and then adjusted by taking into account the genetic level of the contemporaries. These estimates depend on the genetic level of the herdmates. A modification of the procedure in which account is taken of the herdmates' genotype before regressing for small numbers would remedy this deficiency without increasing computing costs.

Twenty-four lactating cows were used in a 6-week randomized block experiment to assess the effect of replacing 2·4 kg of cereal-based concentrate dry matter by either 2·6 or 3·2 kg of kale dry matter for cows with ad libitum access to grass silage. Milk yield, milk composition and live-weight change were not affected by the inclusion of kale. Silage dry-matter intake was significantly lower on the kale treatments than with concentrate, being 8·51, 7·89 and 7·95 kg per day for the concentrate, low-kale and high-kale supplements respectively. Energy digestibilities were 68·1, 74·4 and 76·4% and nitrogen digestibilities 67·1, 74·9 and 78·8% for the three treatments respectively.

Two trials with 44 and 30 British Friesian male calves were conducted over a period of 48 and 30 weeks respectively, to study the value of dried citrus pulp and grape marc as substitutes for part of the barley in calf-fattening diets. In each case the diets were fortified with additional crude protein to compensate for the lower digestible crude protein contents of these substitutes.

Including dried citrus pulp at 60% of the concentrate diet had no effect on calf performance or feed intake, and provided additional protein is supplied, citrus pulp appears to compare favourably with barley as an energy source.

Inclusion of grape marc at 15 and 30% of the diet tended to reduce live-weight gain at the higher level and to reduce killing-out percentage and increase feed intake at both levels, resulting in poor feed utilization. Its value as an energy source appears to be about half that of barley.