The calving rates, survival and growth of calves of Brahman (344), Bonsmara (454), Simmental (601) and Tuli (276) crossbred cows, and pure Tswana (405), were collected for a 7-year period, 1974–80. Calving and survival rates for calves were 0·90, 0·88, 0·87, 0·87 and 0·82; and 0·94, 0·93, 0·96, 0·94 and 0·93, for Simmental, Tuli, Brahman and Bonsmara crossbreds, and pure Tswana, respectively. These differences were not significant (P<0·05).

Calves produced by Simmental ♂ and Bonsmara ♂ crossbred cows were significantly heavier than those from Brahman ♂ and Tuli ♂ crossbred cows (P<0·01), but not from Tswana-sired calves. At weaning, calves from Simmental-cross cows weighed 214 kg, significantly heavier than those produced by any other cow type (P<0·01). Bonsmara- and Brahman-cross cows produced calves weighing 203 and 198kg respectively at weaning, which were also significantly heavier than the calves of Tswana and Tuli crossbred cows (P<0·01), which weighed 187 and 184 kg respectively.

Productivity estimates combining these three traits, and expressed as weight of calf weaned per cow per year, per kg cow weight and per kg metabolic weight of cow, demonstrate the advantages of three of the crossbred cow types over the pure Tswana. Recommendations for the further development of crossbreeding systems in Botswana are made on the basis of this finding.

In 40 ewes exposed to thermoneutral or cold environments during the last 5 to 6 weeks of pregnancy (experiment 1), and in 10 ewes treated in the same way during the last 3 to 9 days of pregnancy (experiment 2), cold exposure lengthened mean gestation times by 1·7 and 2 days respectively. This effect was statistically significant only in experiment 1. Blood samples were taken from the right atrium of ewes in experiment 2 and the concentrations of some hormones in the plasma were measured. Cortisol concentrations were higher in plasma from cold-exposed ewes than control ewes. Plasma progesterone concentrations were lower in cold-exposed ewes than control ewes during a period from 36 h before parturition to 36 h after parturition, but the changes in plasma total unconjugated oestrogens, 17a, 20o-dihydroxypregn-4-en-3-one and oestrogen sulphates were associated with parturition in the normal way.

The mechanism underlying the prolongation of gestation during cold exposure requires further investigation; events that precede the change of steroid production by the placenta at parturition are most likely to be involved.

The proportion of whole grain consumed that was voided intact in the faeces of ewes in late pregnancy and early lactation was measured for diets based on a range of forages in two experiments. The proportions of grain voided intact varied widely between ewes and was to some extent a characteristic of the individual ewe. During late pregnancy on hay-based diets the mean proportion of grain recovered was 0·053 with a range from 0·042 to 0·063 while on silage-based diets 0·135 (range 0·082 to 0·209) was recovered. On silage-based diets after lambing 0·196 and 0·235 of grain was voided intact in the faeces. The proportion of intact grain voided was affected by forage intake. The estimated increase in the proportion of grain voided intact was 0·012 measured over a range of forages before lambing and 0·021 on silage after lambing per 100 g increase in dry matter intake. However, when the total digestibility was measured, there were no differences between feeding of whole and processed grain where proportionately 0·06 of whole grain consumed was voided intact.

Regression equations relating the intake factor to the dissolved faeces fraction, faecal nitrogen and faecal cellulose contents were derived in a continous digestibility trial with cut herbage, and also with sheep fitted with oesophageal fistulae grazing the pasture from which the herbage was cut. In the grazing trial the intake factor was calculated from the in vitro digestibility of the fistula samples.

The relationships established in the digestiblity trial differed significantly (P<0·001) from those in the grazing trial. These differences may have arisen from selective grazing or from bias in estimating digestibility from fistula samples.

The digestibility of the diet selected in the grazing trial was estimated from the various faecal index relationships established. These estimates were very variable. In contrast there was reasonable agreement between estimates derived by the fistula technique and those predicted from a ‘general’ relationship between the intake factor and faecal nitrogen as established at this Laboratory with a wide range of herbages.

It is concluded that faecal index relationships must be derived with material similar to that selected by the sheep when grazing.

Three pig trials were done to estimate an objective requirement of young (10 to 20 kg) pigs for leucine (Leu). Within each trial, four or five replicates of five pigs were given ad libitum access to their experimental diet for a period of 21 (trial 1) or 19 days (trials 2 and 3). A Leu-deficient diet (177 g crude protein per kg) based on maize, peanut meal, lactose, sucrose, dried whey, maize starch, soya-bean meal (SBM), and gelatin was used in these trials. Trial 1 showed that the Leu-deficient diet supplemented with Leu produced responses in weight gain and gain/food ratio that were similar (P > 0·10) to that obtained from a maize-SBM-whey positive-control diet containing 213 g crude protein (CP) per kg. Trials 2 and 3 utilized graded levels of crystalline L-Leu to determine the minimal Leu requirement in young pigs. Both trials showed linear increases (P < 0·05) in weight gain and gain/food as a result of Leu supplementation. Closer examination of the data revealed no significant change in gain/food or PUN responses above 11·2 g/kg total Leu in trial 2, or in weight gain or PUN values above 11·5 g/kg total Leu in trial 3. These data indicate that the Leu requirement of young pigs is probably not greater than 11·5 g/kg (10·5 g/kg true digestible), which equates to approximately 0·72 g true digestible Leu per MJ metabolizable energy. The ideal ratio of Leu to Lys appears to be close to 1: 1 for pigs in the weight range of 10 to 20 kg.

Studies of rectal temperature changes in Blackface lambs from birth to 24 hr indicated a very limited effect within an ambient temperature range of 28 to 66°F. The rectal temperature of twins at birth was lower than that of singles, but the difference disappeared by 3 hr after birth. Body weight was correlated with rectal temperature at birth only in twins. In both twins and singles there was an elevated level of rectal temperature after birth which was presumably associated with a postnatal rise in metabolic rate similar to that which occurs in other species. It is concluded from the results that heat regulation is completely developed within a short interval of birth.

Changes in body weight at intervals up to 48 hr were small, and body weight was significantly different from that at birth only at 48 hr in single lambs.

Relative growth of length and thickness of femur, tibia, humerus and radius-ulna was studied using data from 320 rabbits from both sexes of two lines (New Zealand White and California). A cross-sectional design was used with slaughter points fixed at weekly intervals from 1 to 20 weeks of age. Carcass length was chosen as independent variable and two models were fitted to the data. Model 1 assumed the existence of one allometric change at some moment of the post-natal development and model 2 of a continuous change of the allometric coefficient throughout the experimental period.

Most of the bone measurement showed allometric changes and in all the cases they were not abrupt but continuous. The theoretical and practical implications of the existence of these changes are discussed. The allometric coefficients of all the bone measurements showed a decreasing rate of change except radius-ulna thickness. While the coefficients for bone lengths were positive tending to isometry, for bone thickness they were always negative.

This paper is an attempt to throw a little light on what is probably the most neglected, and yet most important aspect of Artificial Insemination, namely, the management of the bulls used for this purpose.

Evidence is becoming apparent that a number of bulls used for A.I. have been discarded or compulsorily rested because they refused service. As the number of Centres increases so will the number of bulls which fall into this category, and the problem is likely to be the greatest that A.I. has to face in the future.

It is rapidly becoming obvious that this failure of sex drive is not, as generally thought, primarily nutritional, but is in a large degree due to the lack of knowledge of the psychological process involved in the sexual act, and the consequent ill-handling of the animals during service. The knowledge available on the mental processes which take place is inconclusive and complicated, and involves androgenic and oestrogenic factors and their relationship with these processes.

The objective of this study was to calculate cumulative discounted expressions (CDE) for Japanese Black sires carrying a single defective allele in a herd by applying the gene-flow method to investigate the expression pattern of homozygous recessive genotype and to evaluate the monetary loss of using these sires. A single biallelic locus was considered with A representing the dominant allele and a representing the recessive allele. The gene-flow method was modified to consider the fitness of homozygous recessive genotype. Input parameters representing a typical situation in a Japanese Black cattle herd were used to calculate the CDE and the loss of using carrier sires. The effects of initial allele frequency and fitness on the CDE were determined for Aa and AA sires. The CDE of Aa sires were larger than those of AA sires under all initial allele frequencies and fitness. The difference in the CDE between using Aa and AA sires was largest when fitness was 0 (lethal recessive condition). The differences in the loss between Aa and AA sires were larger with increasing initial allele frequencies in lethal recessive condition. Applying the method used in this study to defects reported in Japanese Black cattle and with a population size of 628 000, the difference in the loss between using Aa and AA sires was US$48 575 800 and US$74 418 000 in the case of Band-3 and Claudin-16 deficiencies, respectively. The approach used in this study could be applied to other genetic defects in different breeds and species.

Two experiments were carried out with 12 non-pregnant, non-lactating beef cows (Simmental x Hereford cross), six in each experiment. In experiment 1, the cows were grazing stubble pasture and each cow was hand fed 750 g/day soya-bean meal. In experiment 2, the cows were grazing green pasture at the pre-blossom stage. Paraffin-coated magnesium ferrite (MF) was used as an external marker. A capsule containing 5 g marker was administered to each cow twice daily at about 08.00 and 14.00 h. At the same time the cows were also weighed and faecal grab samples (GS) were taken. Each experimental period lasted 18 days: a 10-day period for attaining steady state of the marker, followed by an 8-day period during which faecal GS were taken.

Average live weight (LW, kg) and daily faecal output (DFO, kg dry matter (DM) per day) were, respectively 364·2 and 3·39 for cows in experiment 1, and 484·4 and 4·62 in experiment 2. DFO (g): LW (kg) ratios were 9·31: 1 and 9·53: 1 in experiments 1 and 2, respectively.

In-vitro digestibilities were used for calculating the voluntary intake (kg DM per day), which was found to be 6·8 and 13·6 for cows grazing stubble and pre-blossom pastures, respectively. The relationships between LW of grazing cattle and their DFO and voluntary food intake are discussed.

Lamb mortality in a Scottish Blackface hill sheep flock subjected to long term selection for cannon bone length and fleece medullation score was investigated, using maximum likelihood analyses. The selection for cannon bone length and for medullation score had no significant effect on lamb mortality.

The objective was to determine the effects of avoparcin, bovine somatotropin (bST) and the additive effects of both avoparcin and bST on milk yield, milk composition, live-weight changes and reproduction parameters in post-partum dairy cows. Forty-eight autumn calving cows were allocated using a split-plot within randomized complete-block design to the following treatments: (i) control (2 ml saline plus 1 kg untreated concentrate per day); (ii) avoparcin (2 ml saline plus 1 kg concentrate containing 100 mg avoparin per day); (Hi) bST (25 mg bST in 2 ml saline plus 1 kg untreated concentrate per day); and (iv) avoparcin plus bST (25 mg bST in 2 ml saline plus 1 kg concentrate containing 100 mg avoparcin per day). All injections were given subcutaneously and treatment continued for 84 days beginning 55 (s.e. 4) days after calving. The cows were offered grass silage ad libitum supplemented with 7·2 kg cereal-based concentrates daily. Milk yield and milk composition were measured thrice and once weekly, respectively. The cows were weighed and body condition score was assessed every 2 weeks.

Mean daily milk yield of cows assigned to control was 20·1 (s.e. 1·5) kg, avoparcin, 21·5 (s.e. 1·5) kg, bST, 23·9 (s.e. 1·0) kg and avoparcin plus bST, 25·2 (s.e. 1·2) kg over the 84 days of the trial. bST increased milk yield proportionately by 0·18 compared with all cows not given bST (P < 0·01). Avoparcin did not significantly increase milk yield. There was no effect of any treatment on milk composition, body weight or body condition score. None of the experimental treatments had any effect on calving to first service interval, calving to conception interval, number of services per conception or overall conception rate.

These results show that in early lactation, avoparcin alone had no effect on production or reproduction parameters in dairy cows; bST alone increased milk yield but did not affect any other production or reproduction parameter. There was no significant additional increase in milk yield when avoparcin and bST were given in combination, compared with bST alone.

Forty entire male pigs, between 63 and 147 days of age, and weighing initially 21 kg, were given a basal diet containing 1·8 g methionine per kg, and based on wheat, sorghum and lupin-seed meal (Lupinus augustifolius cultivar Unicrop), supplemented with 0, 0·2, 0·4 or 0·6 g methionine per kg.

Supplementing each kg of the basal diet with 0·2 g methionine per kg significantly increased growth rate by 105 g/day and improved efficiency of food conversion between 21 and 35 kg live weight. Increasing the supplementation of methionine to 0·6 g methionine per kg diet increased growth rate between 21 and 35 kg live weight by a further 26 g/day but did not affect efficiency of food conversion. Between 35 and 71 kg live weight, performance was not improved by supplementation of the basal diet with methionine.

It has often been said that “grass is the cheapest and healthiest feed we can offer our farm animals.” There is a fairly good body of evidence and some consensus of opinion that grass is a cheap food (see J. R. Currie, 1948, J. Brit. Grassl. Soc, 3:27).

Grass fed in situ is cheap for us in Britain, because it is a crop which in terms of nutrients per acre either tops the list or is always in the higher yield group among our farm crops. This is true whether we base our comparison on starch equivalent or on nitrogen (expressed as crude protein). Productive grassland is always high in its comparative values.

The following table will serve to emphasise this point.

This table is based on data published in 1941 by Leeds University, and is an example of the sort of figures frequently given in respect of different crops.

Although the amount of food given to dry sows in commercial situations is nutritionally adequate for maintenance and reproductive performance, it may not be adequate in other aspects. There is evidence that low levels of food intake increase the incidence of abnormal behaviours. It might be desirable to feed greater amounts, but without causing excessive nutrient intake and obesity of the sow which occur when feeding commercially used diets at high levels. One solution might be to provide bulky, low density diets. The objectives of this experiment were to obtain information on level and variation in voluntary food intake in dry sows on fibrous diets and on the relationship between chemical aspects of the diet, intake, and apparent digestibility.

The optimized use of dietary nutrients and the accurate knowledge of the growth dynamics of body components is important for efficient pig production. This study aimed at evaluating the growth of carcass components and organs of Swiss Large White pigs from birth to 140 kg BW depending on the CP and amino acid (AA) supply. A total of 66 entire males (EM), 58 castrates (CA) and 66 female (FE) pigs were used. From 20 kg BW onwards, they had either ad libitum access to a control (C) or a diet (LP) with 20% lower CP, lysine, methionine + cystine, threonine and tryptophan content compared to C. The weight of organs, primal cuts and external fat were recorded in eight EM and eight FE; at 10 kg BW, on two EM, CA and FE each, and at 20 kg BW, on eight pigs from each sex. From 40 to 140 kg BW at 20 kg intervals, measurements were recorded on four pigs per sex and dietary treatment. The weight of each component was related to empty body (EB) using allometric regressions. Kidneys were heavier (P<0.05) in C- than LP-pigs and in EM than CA and FE. Above 21 kg EB weight, growth rate of LP-FE overpassed (P<0.05) the one of C-pigs. Consequently, LP-FE had heavier (P<0.05) lean cuts than C-pigs in the finisher period. However, LP-CA and LP-EM displayed lower (P<0.05) weights and growth rates of the lean cuts than C-CA and C-EM. Shoulder and loin weights and growth rates were reduced (P<0.05) in LP-pigs when compared to C-pigs. Growth rates of the ham were greater (P<0.05) in LP-FE than C-FE, whereas in LP-EM and LP-CA they were lower (P<0.05) than their C-counterparts. Total amounts of subcutaneous fat, backfat, ham fat and shoulder fat were lower (P<0.05) in C- than LP-pigs. The total amount of subcutaneous fat, backfat and shoulder fat of C-CA was, regardless of diet, greater (P<0.05) than of C-FE. In the LP group, this difference was even more pronounced. The amount of deposited ham fat was greater (P<0.05) in LP-CA than LP-FE, but not in C-CA v. C-FE. Differences in kidney weights suggested a greater nitrogen clearance required in C-pigs. Overall, dietary restriction and sex did not affect all body parts to the same extent. This study further suggests the possibility to reduce the CP and AA supply in FE without compromising the yield of primal lean cuts or increasing the amount of subcutaneous fat.

In three successive experiments 32, 30 and 32 autumn-calving, single-suckled cows were subjected to individual planned weight reductions over winter on silage-based diets with various levels of concentrate supplement. At a similar level of weight loss, milk yield and calf gain were increased when protein supplements of low rumen degradability were given. On average, the inclusion of 0·75 kg fish meal in the diet improved calf gain by 0·13 kg/day. Results are discussed in terms of the effect of protein supplement on the efficiency of use of body reserves.

We conducted an experiment to determine whether early-life social learning of feeding site selection in lambs was sex-specific. Sixteen ewes and their new born lambs were used in a controlled experiment. Eight ewe–lamb pairs included a male lamb and the remaining eight a female lamb. All pairs were individually exposed to an experimental arena containing a safe and unsafe artificial feeding site (SFS, UFS) each consisting of nine bowls which contained either ground Bermuda grass hay (SFS) or ground alfalfa hay (UFS). The bowls in UFS were surrounded by bright orange traffic cones (visual cues). Half the ewes were trained with controlled electric shock to avoid UFS. Thus, pairs were randomly assigned to: (1) shock aversion training (SAT) to mothers of male lambs (MS); (2) SAT to mothers of female lambs (FS); (3) no aversion training (NAT, control) to mothers of male lambs (MC); and (4) NAT (control) to mothers of female lambs (FC). None of the lambs were subjected to SAT. During training, testing, extinction, and retraining ewe–lamb pairs were exposed to the arena together. Ewes were then removed from the experiment and two additional extinction phases were conducted with weaned lambs alone. Fear conditioning elicited UFS avoidance of both the trained ewes (means±s.e.m. % times observed in UFS during testing phase: FC=95.3±1.70; MC=94.4±4.87; FS=1.6±1.63; MS=0 ±0; P<0.01) and their naïve lambs (FC=83.8±6.07%; MC=76.6±6.56%; FS=30.4±7.90%; MS=33.9±9.23%; P<0.01). UFS avoidance in lambs occurred regardless of sex and tended to persist after weaning (% times observed in UFS during 1st post-weaning extinction phase: FC=92.6±4.50%; MC=89.8±6.09%; FS=45.1±10.57%; MS=43.5±10.42%; P=0.06). Fear conditioning in mothers appeared to alter sex-related differences in mother–infant behavioral synchrony by increasing and decreasing feeding synchrony of male and female lambs, respectively (FC: r=0.52, P<0.01; MC: r=−0.02, P=0.86; FS: r=0.14, P=0.26; MS: r=0.46, P<0.01). During the extinction phase mothers of ram lambs were observed feeding more often (FC=85.0±2.33%; MC=92.7±1.45%; FS=47.3±8.81%; MS=72±5.68%; P=0.02) and standing less often than ewes with daughters (FC=7.3±2.40%; MC=2.7±0.83%; FS=39.3±9.04%; MS=18.0±5.29%; P=0.06). This study suggests that social conditioning at an early age could be a viable tool to induce learning of feeding site avoidance in female and male lambs alike.