The effects of feeding monensin and amicloral at 33 and 1500 mg/kg of diet, respectively, were investigated in two experiments using 330-kg steers. Monensin and amicloral, either alone or in combination, increased the digestibility of organic matter and crude fibre compared with a control diet (P < 0·001). Crude protein digestibility was increased by monensin (P < 0·001). Use of monensin and amicloral, alone or in combination, increased molar proportions of propionic acid by 22% on average (P > 0·05), and monensin decreased butyric acid by 37% (P < 0·05).

Ruminal ammonia concentrations were lower in steers fed monensin (P < 0·05). Steers fed monensin consumed 6 % less feed, gained 9 % more weight (P < 0·05) and utilized feed 14% more efficiently (P < 0·05) than control animals. Amicloral, either alone or with monensin, lowered feed intake by 11 % (P < 0·05), had no effect on average daily gain and improved feed efficiency by about 12% (P < 0·05). There were no treatment effects on any of the carcass parameters.

A preliminary trial established a subclinical level of infection with Oesophagostomum dentatum capable of affecting the performance of growing pigs. Thereafter a slightly higher level of infection (100 000 larvae) was administered to each of 24 individually- and scale-fed pigs to investigate the effect of O. dentatum on performance, digestibility and nitrogen retention over the live-weight range 32 to 64 kg. Worm-free but otherwise similar pigs served as controls. Infection reduced growth rate (12·9 %) and decreased efficiency of feed conversion to body weight (14·9%). There was no effect on killing-out percentage or area of eye muscle in cross-section, but infected pigs had relatively lower backfat depths (5·5 to 12·5 %). Infection did not influence nitrogen retention, but apparent digestibility of the dry matter, organic matter, nitrogen, gross energy and crude fibre was reduced. Possible explanations for these effects are discussed in relation to tissue changes associated with larval development in the large intestine.

Twenty-six groups of four or eight pigs of mean initial weight 23·2 kg and mean age 84 days were exposed to environmental temperatures of 8, 12, 16 or 20°C under still-air conditions (wind-speed = 0·1 m.s−1) or of 12CC with wind-speeds of 0·45 or 0·8 m.s−1. The animals were fed at a fixed level close to three times their maintenance requirement, with water ad libitum, and were weighed weekly over a 7-week period. Variation in temperature between groups from 8 to 20°C had no significant effect on weight gain, but increasing wind-speed to 0·8 m.s−1 at 12°C resulted in reduced weight gain.

In order to investigate the effects of type of breed on carcass composition, an examination was made of 361 lambs from four breeds: Clun Forest and Colbred (termed ewe breeds); and Suffolk and Hampshire (termed ram breeds). The animals were in four carcass weight groups averaging 15, 17, 19 and 21 kg.

Percentage subcutaneous fat was influenced more by carcass weight than by breed, whereas both carcass weight and breed had similar effects on percentage lean. At the mean carcass weight of 18 kg, Colbreds, the leanest breed, had a similar value for percentage lean (about 57 % of carcass tissue weight) to the carcasses over all breeds weighing 15 kg; and Cluns, the fattest breed, had a similar value (about 54%) to those weighing 21 kg. Since the ram breeds were intermediate in composition between the two ewe breeds there was no effect of type of breed on carcass composition. The breed differences were related to eventual mature size and to the stage of maturity at each carcass weight, as judged by body length and bone weight measurements. However, Colbreds were bigger and leaner than published estimates of their mature weight suggested. Humerus weight was a good predictor of lean or total fat weight, explaining 83 % ofvariation when used as a predictor along with carcass weight.

Type of breed had a marked effect on internal fat deposition, the ewe breeds having heavier weights of both kidney knob and channel fat (KKCF) and caul fat (omental fat) than the ram breeds; and on the length oflimb bones, the ewe breeds having longer but thinner bones than the ram breeds. The order of the relative growth of the tissues and fat depots was: subcutaneous fat > caul fat > KKCF > intermuscular fat > lean > bone. Therefore, the internal fat depots were later maturing than intermuscular fat.

The percentage of prime cuts in the carcass was not affected by carcass weight. Colbreds had significantly lower values than the other breeds. Suffolks had the lowest lean to bone ratio.

Seasonal fluctuations in oestrous activity and live weight were studied in ewes of the Marwari breed indigenous to the Rajasthan Desert in north-western India. Of the ewes examined 80 to 100% were in oestrus every month of the year, indicating thereby the non-seasonality of female reproductive activity in this breed. On average, each ewe exhibited heat 18 times a year. The incidence of silent heats was low (4·2 %). The average length of an oestrous cycle was 17 days, while the actual period of oestrus varied from 24 to 48 h with an average of 36 h. No seasonal effect on these activities could be observed. The maximum and minimum body weights of the animals were recorded during the autumn (October) and summer (June) months respectively. The body weights differed significantly (P<0·05) between months. Sexual activity in these animals is, therefore, apparently not affected by changes in body weight. The continuous nature of oestrous activity in Marwari sheep may be economically exploited by regulating the lambing season according o t the prevailing ecological conditions and market demands, without the use of hormones.

In the year ending September 1977, 242 British Friesian cows were recorded as having produced more than 10 000 kg in a 305-day lactation. The model y(n) = anbe−cn was fitted to the monthly test day yields of each lactation (a, b, c are constants, e the base of natural logarithms and y(n) the average daily yield in week n). The model explained 87·7% of total variation in the loge y(ri), and the mean constants were 31·8, 0·3160 and 0·0373. Seasonality of production was confined mainly to a spring peak of about 10% above an approximately constant level of production during the rest of the year. These lactations generally peaked later, were more persistent and showed less response to seasonal variation than average.

In two experiments young British Friesian cattle were allowed restricted access to maize silage on a self-feed system. Restrictions were imposed by either limiting the width of feed face per animal or by reducing the time available for feeding.

The social order of each group of cattle was determined by observing dominance-submission interactions between pairs of individuals. Dominance rank and angular dominance values were calculated for individuals in each group and related to silage intake, feeding time and rate of eating. Silage intake and rate of eating increased significantly with dominance value, and feeding time decreased although not significantly.

Micronization followed by grinding of brown-seeded sorghum increased starch availability in vitro but had no effect on proximate composition of the grain. In diets containing 70% of sorghum in ground or micronized and ground form, apparent digestibility of dry matter and nitrogen and nitrogen retention by growing pigs were improved (2·5, 5·0 and 12·2% respectively). Addition to the diet of 0*2 g polyethylene glycol per g crude protein in the sorghum fraction produced similar effects. In the ground cereal diet inclusion of polyethylene glycol increased apparent digestibility of gross energy (3·8%) and improved metabolizable energy content by 5·5%, but i n the micronized and ground cereal diet the additive had no effect.

Soay ewes were mated to a Soay or a Dorset Down ram. Live-weight changes of the ewes, birth weights, growth rates and carcass production of the lambs were recorded, and the food consumption of the ewes and lambs was measured. The use of the Dorset Down ram resulted in significantly heavier birth weights, higher growth rates and heavier carcasses. Under conditions of good nutrition the Soay ewes proved to be capable of carrying very high foetal burdens and it was estimated, from lamb live-weight gains, that they produced a large quantity of milk, relative to their size, particularly when crossed with the Dorset Down ram.

ANIMAL PRODUCTION, Volume 28, Part 2, pp. 157-170

GROWTH, FOOD INTAKE AND COLD EXPOSURE IN MICE

1. Cold Exposure of Adolescent Mice

N. Bateman and J. Slee

Sixteen male and 16 female lambs were used to compare the performance and carcass composition of Texel- and Suffolk-sired lambs out of Finnish Landrace × Dorset Horn ewes. Lambs were weaned at 6 weeks of age and individually fed an all-concentrate diet ad libitum to slaughter at 30 kg (females) and 36 kg (males). At slaughter, offal weights were recorded and carcass left sides jointed and dissected.

Breed types did not differ in weight at weaning, growth iate, age at slaughter, daily feed intake or feed conversion rate. Texels had heavier carcasses (17·2 v. 16·4 kg: P <0·01) and higher dressing percentages (50·7 v. 49·2: P <0·05) than Suffolks. Texel-cross carcasses had 2·9% more lean (P <0·05), but 3·8% less total fat CP <0·01).

The results indicate the suitability of Texel-sired lambs for intensive lamb production.