The amylase (Am I) genotypes have been determined in sera from 834 cows comprising 562 Friesians, 77 Ayrshires, 106 Guernseys, 62 Jerseys and 27 crossbred cows. All of these cows had completed their third lactation and many were much older. There was a highly significant excess of heterozygotes at the Am I locus. This excess of heterozygotes was highest in high-yielding Friesian herds and there was a significant correlation between percentage heterozygotes and herd yield in the Friesians.

1. Four British Friesian steers were reared to a live weight of 340 kg as pre-ruminant animals, by the use of milk substitutes based on liquid skim milk, spray-dried whey powder and an ultra-high-fat (68%) milk powder.

2. Except for one case of hypomagnesaemia, the steers remained healthy. Live-weight gain/day, age at slaughter and feed conversion ratio were 1·23 kg, 253 days and 2·31 kg dry matter/kg weight gain respectively.

3. No marked development of the rumen had occurred; gut fill in relation to fasted live weight was 3·4% and killing-out percentage was 61·2.

1. Three groups of six castrated male cattle aged 6,18 and 36 months and three corresponding groups of sheep received in turn three diets consisting of high-quality dried grass (A), low-quality grass (B) or 60% of B with 40% barley (C). For one-half of each 6-week period the grass was eaten in the long form (L) and for the other half, it was ground and pelleted (P).

2. Pelleting increased intake by 45% in sheep, from 56·8 to 82·4 g dry matter per kg W-75 per day, but only by 11% in cattle, from 81·8 to 90·7. The increase was greater for diet B (44%) than for A (19%) or C (15%), and greater for the youngest animals (38%) than for the middle-aged (17%) or oldest (20%).

3. Dry-matter digestibility was reduced by pelleting from 67·2% to 58·6% in sheep and from 69·9% to 56·9% in cattle. The reduction was greater for diets A (71·2% to 56·1%) and B (65·7% to 54·1%) than for diet C (68·7% to 63·2%).

4. A hypothesis based on the importance of particle size of digesta leaving the rumen provides a possible explanation ofthese interactions between form of roughage on the one hand, and species and age of animal or diet composition on the other.

An experiment designed to study the response in milk production to dried grass given as an addition to a basal roughage diet and to assess its value as a replacement for conventional dairy concentrates is described. A randomized block design with 34 lactating cows was used. The cows received supplements of either dried grass (dry-matter digestibility, 70%, 0·28, 0·39, 0·50 or 0·61 kg/kg milk) or a cereal-based dairy concentrate (0·39 kg/kg milk) in addition to silage offered in amounts to meet the maintenance energy requirements. Milk yield, milk energy output, live-weight gain and the fat, solids-not-fat and protein contents of the milk increased with level of addition of dried grass. Interrelationships between the level of feeding of dried grass and milk output and body-weight change are given. The derived relationships between dried grass input and animal output were used to predict the replacement value of dried grass for conventional dairy concentrates. These indicated that dried grass offered at 042 kg/kg milk would produce equivalent milk yield and body-weight changes to concentrate given at 0·39 kg/kg milk. Ration digestibility and nitrogen balance results are also given.

The effectiveness of silastic rubber implants impregnated with melengestrol acetate (MGA) to suppress heat in heifers being finished for beef was tested. Nine uniparous females received MGA implants, nine received 0·5 mg MGA orally and eight similar non-treated animals served as controls for a 110-day experimental period. Based on occurrence ofheat and ovarian examination during treatment and at slaughter, the silastic implants were effective in suppressing heat throughout the experimental period. The animals with implants also had a significantly higher rate of daily gain than the controls (P<0·1). In a second experiment the implants were effective in suppressing heat but the increase in daily gain did not reach significance. Silastic implants of MGA are effective for the long-term suppression of oestrus in finishing heifers and their effective life span is sufficiently long for use under commercial farming conditions.

Apparent mortality among 280 215 embryos from the 4th to 16th week of gestation was studied from returns to service records following first inseminations with fresh semen from 100 bulls of five dairy and three beef breeds of cattle over a period of 8 years.

The average incidence of apparent mortality was 20·3% for embryos conceived by fresh semen first inseminations. Differences in rates of apparent embryonic mortality between breeds of sire and also between sires within the Guernsey, Ayrshire and Dairy Shorthorn were statistically significant although confounded with the breed of dam. The highest incidence was from matings by bulls of the Channel Island breeds. These results suggest that hereditary factors influenced embryonic mortality in cattle.

The rate of apparent mortality was higher among embryos conceived by frozen semen than by fresh semen. Ageing of fresh semen extra-corporeally also increased the rate of apparent embryonic mortality but to a lesser extent than frozen semen.

The rate of apparent embryonic mortality increased with the greater number of inseminations required for conception possibly because of a deteriorating maternal environment.

Concentrations of copper in blood plasma were determined in January and in February 1971 and in February and March 1972 in a grassland flock of sheep comprising the Finnish Landrace and (Tasmanian) Merino breeds and their reciprocal crosses. Numbers of animals ranged from 30 to 100. The unadjusted mean copper levels of the flock varied from 63 to 81 μg/100 ml. The Finnish Landrace had a markedly lower plasma copper concentration than did the Merino, the mean difference after adjustment for other factors varied from 16 to 54 μg/100 ml. First crosses had levels halfway between those of the parental breeds. Copper concentration fell in the 4-week period between February and March 1972 when most of the ewes were pregnant. This fall was greatest for the Finnish Landrace which started with the lowest level and least for the Merino.

Neither the breed differences in the change in level nor the actual concentration appeared to be related to the number of lambs (0 to 4) carried by the ewes. Variation in copper level associated with the age of ewe, significant for the two bleedings in 1972, was largely attributable to the higher level among the youngest age class, approximately 10 months old when bled. The stage of pregnancy at the time of blood sampling, as reflected by date of lambing, did not significantly affect plasma copper concentration in this flock.

The delayed onset of heat-induced panting (at 42°C) immediately following previous shearing and exposure to cold was studied in 54 Scottish Blackface and 53 Tasmanian Merino sheep.

In control sheep (not previously cold-exposed) thermal panting commenced in 15 min. In cold-treated sheep, when the cold was intensified stepwise from +26°C (+30cC being thermoneutral) down to −10°C, using 2-hr exposures, or lengthened from 2 hr to 16 hr at +8°C, the delay (block) to panting increased non-linearly from 40 to 70 min.

The minimum intensity of cold required to produce a block (26°C in Merinos, 22°C in Blackfaces) was similar to that inducing peripheral vasoconstriction. More intense vasoconstriction preceded longer blocks, but vasoconstriction sometimes occurred without a subsequent block.

Merinos were more sensitive than Blackfaces to the blocking effects of cold, and, once blocked, the effect in Merinos was less easily removed by re-warming.

The time taken for cancellation of the heat debt during heat stress could account for half the block. The remainder, a delay of about 30 min, was attributed to a specific inhibition of respiratory control in the central nervous system.

Estimates were made of milk and herbage intakes and growth rates of male lambs born to Merino ewes which had been mated to Merino, Border Leicester, Corriedale, Dorset Horn or Southdown rams. The lambs were castrated and with the ewes grazed grass-clover pastures at two stocking rates.

Crossbred lambs consumed more milk and more grass, and grew more rapidly than Merino lambs. The greatest intakes and growth rates were attained by progeny of Border Leicester and Dorset Horn sires; Corriedale and Southdown crosses also grew more rapidly than Merinos.

Lambs at the high stocking rate received slightly more milk and consumed less grass than those grazed at the low stocking rate. The growth rates of groups were similar.

In the first experiment two groups of 11 Scottish Blackface ewes were given either 6·10 kg dried grass pellets plus 1·63 kg chopped dried grass daily (Group A) or 8·17 kg hay plus 1·32 kg oat pellets (Group B). During a 10-day experimental period individual dry-matter intakes ranged from 484 to 939 g/day (CV 22·3%) in Group A and from 613 to 883 g/day (CV 13·3%) in Group B. In Group B dry-matter intakes from oats were much more variable (10 to 149 g/day; CV 35·8%) than those from hay (530 to 762 g/day; CV 12·9%). Plasma protein-bound iodine (PBI) concentrations were significantly higher in the Group A sheep.

In the second experiment the treatments were: group-penned, group-fed (GG); group-penned, individually fed (GI); and individually penned, individually fed (II). Within each treatment there were two groups of 12 ewes; one group was given a high level of feeding (H) and the other a low level (L) for a 7-week experimental period. Allowances of pelleted concentrates ranged from 7 to 15 g/kg in the L groups and from 18 to 26 g/kg in the H groups. The same mean quantities per kg were given to GG sheep, and food intakes ranged from 5·7 to 17·7 g/kg (CV 25·3%) in GGL and from 12·5 to 30·8 g/kg (CV 24·8%) in GGH. Plasma PBI concentrations were significantly higher in L sheep than in H sheep, and higher in GG than in II. Plasma non-esterified fatty acid concentrations were significantly higher in L sheep than in H sheep and higher in GG than in GI and II.

The principal factors determining variations in food intakes between individual animals fed in groups and some of the nutritional implications of group-feeding sheep are discussed.

Digestion trials were conducted with four ponies, two sheep and two New World camels (one llama and one guanaco) given alfalfa pellets and a complete pelleted hay-grain diet. The New World camels were significantly more efficient in the digestion of dry matter, neutral-detergent fibre, acid-detergent fibre and cellulose than the sheep or ponies.

The fatty acid composition of milk samples from Ayrshire twin cows was determined. The results were in general agreement with those reported by other workers. Comparisons between the variation within pairs of one and two-egg twins showed that the proportions of different fatty acids are subject to a high degree of genetic control.

Fifty-four Suffolk × North Country Cheviot lambs were weaned at either 25, 33 or 41 days of age and slaughtered at either 35, 45 or 55 kg live weight.

Increasing the age at weaning reduced the growth check, increased creep feed consumption and decreased food required for fattening. For each kg increase in weight at slaughter there was an increase of 0·035 kg in dry matter required per kg gain. The female lambs had lower growth rates, lower efficiency of food utilization and a higher killing-out percentage than male lambs.

For the most efficient utilization of food, lambs should be weaned at about 33 days of age.

Two diets, one based on barley and white-fish meal and the other on oats, wheat and meat and bone meal, with similar concentrations of digestible energy, crude protein, lysine and methionine+cystine were used to investigate the effects of sudden changes in the composition of the diet on the performance of pigs growing from 32 kg live weight, over a period of 77 days.

The diets were given separately, alternated weekly with sudden changes from one diet to the other, or as a 1:1 mixture.

Changes in diet per se had insignificant effects on performance.

Two experiments were carried out in which subcutaneous implants of thyroxine pellets were made into Soay sheep in autumn after the wool follicles had become inactive. This hormonal treatment failed to restore wool growth or to shorten the winter period of follicle inactivity.