African Journals Online
South African Journal of Animal Science

Volume 30, Issue 3, 2000
Abstracts

The effects of shade and shearing date on the production of Merino sheep in the Swartland region of South Africa
Cloete, S.W.P.Muller, C.J.C.Durand, A. 164-171

Abstract: A total of 497 Merino ewes were allocated to one of four experimental groups for the period 1996 to 1998. The treatments were designed to provide data on the effect of shade during an autumn lambing season and the effect of shearing prior to joining in September or prior to lambing in February. Dietary intake in shaded and control paddocks was similar, but animals in shaded paddocks consumed less water than those in control paddocks. Lambs born in shaded paddocks tended to be heavier at birth than those born in control paddocks. Survival of lambs was unaffected by the provision of shade, but lambs born in shaded paddocks were 3.8 % heavier at weaning than contemporaries born in control paddocks. Lambs born to ewes that were shorn prior to lambing tended to be lighter than those from ewes shorn prior to joining. Lamb survival prior to weaning tended to be higher in lambs born to ewes shorn prior to lambing than in those shorn prior to joining. Shearing of ewes prior to lambing had a beneficial effect on lamb survival during 1997, when the survival of progeny of ewes shorn prior to joining was low. Annual lamb survival data obtained in the present experiment were combined with that from two previous experiments conducted at the same site. The response in lamb survival of the progeny of ewes shorn prior to lambing depended on the average lamb survival observed in the control group. Multiple-born progeny of ewes shorn prior to lambing grew faster to lamb marking than contemporaries born to ewes shorn prior to joining. No difference was detected in single lambs. The clean fleece weight of ewes shorn prior to lambing was heavier than that of contemporaries shorn prior to joining. Similar benefits were found for staple strength and the frequency of mid-staple breaks. It was concluded that the shearing of ewes prior to lambing might be advantageous under certain conditions, particularly when lamb survival is likely to be low.

Genetic studies on the South African Mutton Merino: growth traits
Neser, F.W.C.Erasmus, G.J.Van Wyk, J.B. 172-177

Abstract: Genetic parameters were estimated for 36-, 42-, 50-, 100- and 150-day weight in the South African Mutton Merino breed. The direct heritability estimates obtained were 0.270, 0.366, 0.278, 0.185 and 0.115 respectively. The maternal heritability estimates for the respective weights were 0.494, 0.249, 0.129, 0.091 and 0.080. The correlation between the animal effects (direct and maternal) varied between -1.000 for 36-day weight to -0.376 for 150-day weight. Very little selection progress was made over the period (1980-1999) in the breed.

Nutrient partitioning and response to insulin challenge at different planes of nutrition during lactation in goats of high vs. low milk production potential
Cronje, P.B.De Jager, M.Vlok, E. 178-185

Abstract: The aim of this experiment was to determine the effect of genetic selection for milk production on nutrient partitioning at a high vs. a low plane of nutrition. Twelve Indigenous goat does and eight Saanen x Indigenous crossbred does were allocated to either a basal diet formulated to provide energy for maintenance or the basal diet supplemented with maize so as to maintain a plasma glucose concentration of 3.5 mmol/l throughout lactation. Milk yield was not reduced by the low plane of nutrition in either genotype. The sustained rate of milk production at the low level of nutrition was achieved by increased mobilisation of endogenous nutrients from body reserves, evidenced as a greater loss of body mass at the low plane of nutrition in both breeds. The Saanen crossbred genotype, which produced twice as much milk as the Indigenous genotype, lost 19% of initial mass by week 10 of lactation, whereas mass losses in the indigenous goat never exceeded 7%, with the result that repletion of initial (week one) mass was achieved by week six of lactation. Plasma glucose concentrations were depressed to a smaller extent by insulin in the Saanen crossbred than in the Indigenous goat at weeks 3, 7 and 11 of lactation. Although there was evidence for a genotype x nutrition interaction during early lactation, this did not persist throughout lactation. The majority of data derived from this study indicates that the two genotypes reacted in a similar manner to plane of nutrition, with the main differences between milk yield potential being occasioned by differences in the extent of mobilisation of endogenous body reserves mediated by differences in insulin sensitivity.

Genetic parameter estimates for type traits in the South African Jersey breed
Van Niekerk, D.J.Neser, F.W.C.Erasmus, G.J. 186-192

Abstract: Known environmental effects influencing type trait scores in South African Jersey cattle were identified. Variance components and heritabilities were estimated for these traits as well as genetic correlations among them and with production traits. Heritability estimates were generally low to medium. It is suggested that hoof and leg traits be excluded due to low estimated heritabilities and/or coefficients of variation. Genetic correlation estimates suggested that selection for production yield should improve most type traits and vice versa. Estimation of breeding values and fitting a multiple trait model is suggested.

Estimates of crossbreeding parameters in a multibreed beef cattle crossbreeding project
Skrypzeck, H.Schoeman, S.J.Jordaan, G.F.Neser, F.W.C. 193-203

Abstract: Data from purebred and crossbred cattle, consisting of the Afrikaner (A), Simmentaler (S) and Hereford (H) breeds managed in a relatively intensive but high stocking rate environment, were analysed to estimate breed direct effects, individual heterotic effects, breed maternal and maternal heterotic effects for birth weight (BW) and weaning weight (WW). Simmentaler breed direct effects, expressed as deviation from the general mean, were positive (P < 0.01) for both traits. Hereford and Afrikaner breed direct effects were negative (P < 0.01) for both traits while the Afrikaner breed direct effects exceeded those of the Hereford. Afrikaner direct maternal effects were positive (P < 0.01) for both traits. The Hereford direct maternal effect was negative (P < 0.05) (-2.9%) for WW. Simmentaler maternal effect was negative (P < 0.01 ) for BW but non-significant (P > 0.05) for WW. Individual heterotic effects for BW were significant (P < 0.01) in H x S (3.5%) and S x A (11.0%) only. Individual heterotic effects were positive (P < 0.01) for WW, with that of the H x A (9.8%) and S x A (6.7%) crosses exceeding the S x H (3.1%) cross. Maternal heterotic effects were non-significant (P > 0.05) for both BW and WW.

The effect of dietary rumen degradable protein content on veal calf performance
Holtshausen, L.Cruywagen, C.W. 204-211

Abstract: The objective of this study was to determine the undegradable dietary protein requirements of veal calves. Two experiments were carried out with Holstein bull calves from 3-10 days of age until slaughter at 20 weeks of age. Both experiments were divided into starter and finishing periods. Calves were offered starter pellets on an ad lib. basis from seven days of age. Diets were formulated to be iso-nitrogenous and iso-caloric, and differed in undegradable dietary protein content. In Experiment 1 calves were randomly assigned to one of three dietary treatments containing low (LD), medium (MD) or high (HD) levels of rumen degradable protein. In Experiment 2 calves received a starter diet containing either a high or a low level of rumen degradable protein. At the end of the starter period animals from both treatment groups were re-assigned at random to finisher diets containing either low or high rumen degradable protein levels, resulting in four treatment combinations, viz. LL, LH, HL and HH. There were no treatment differences for feed intake, body weight gain or feed efficiency during the starter period of either experiment. During the finishing period (weeks 12-20) of Experiment 1, calves receiving the LD diet had higher average daily gains than calves receiving the HD treatment. Feed conversion ratio for the LD treatment was also better than for the other two treatments. During the finishing period (weeks 11-20) of Experiment 2 the feed conversion ratio tended (P < 0.10) to differ between treatments: feed conversion ratio for the LL and HL treatments was more favourable than that for the LH treatment. Feed conversion ratio for the HH treatment was intermediate, and did not differ from that of the LL, HL or LH treatments. The level of crude protein degradability appears to have no effect on calf performance during the starter period, but it may, however, be beneficial to feed finisher diets with a lower crude protein degradability during the finisher period.

The effect of age on in sacco estimates of rumen dry matter and crude protein degradability in veal calves
Holtshausen, L.Cruywagen, C.W. 212-219

Abstract: This study was conducted to determine whether rumen dry matter and crude protein degradability in calves aged 8-10 weeks differs from that in mature cows. Five Holstein bull calves were rumen-fistulated at six weeks of age and were used in consecutive weekly 24 h trials from 8-20 weeks of age. Dry matter and crude protein degradability of two starter and two finisher veal calf diets of high or low rumen degradable protein content were estimated from 24 h in sacco incubation. Rumen pH and concentrations of volatile fatty acids and ammonia-nitrogen were determined on a weekly basis. Three rumen-fistulated Holstein cows were also used to evaluate dry matter and crude protein degradabilities of the diets. Estimates of dry matter degradability obtained from calves differed between the low and high degradability diets within weeks. Dry matter degradability differed between the starter and finisher diets (weeks 10 and 11) and remained fairly constant from week 11 to week 20. Crude protein degradability in calves also differed between the low and high degradability diets within weeks. Crude protein degradability increased up to week 12 and then remained constant until week 20. Dry matter and crude protein degradability estimates for the starter diets were both lower than the corresponding values obtained with cows, while estimates for finisher diets were similar. There were no clear trends over time for rumen pH, volatile fatty acid concentrations and ratios, or for rumen ammonia-nitrogen concentrations ion calves. These values showed a degree of variation between weeks and were similar to literature values for mature ruminants.

Pre-weaning growth traits of the Hereford breed in a multibreed composite beef cattle population
Skrypzeck, H.Schoeman, S.J.Jordaan, G.F.Neser, F.W.C. 220-229

Abstract: Data from a multibreed composite beef cattle population, managed under intensive irrigated grazing conditions,were used to estimate direct additive heritabilities (h²_a), maternal heritabilities (h²_m) and maternal permanent environmental effects (c²) for birth weight (BW) and weaning weight (WW) of the calf and cow efficiency of the dam (CE: WW/dam weight^0.75 x 100). Calves born between 1968 and 1993 (n = 52628) had varying levels of Hereford genes, ranging from 0% to 100%, with an average of 19.3%. Direct heritabilities, fitting unitrait models, were 0.72, 0.54 and 0.19 for BW, WW and CE, respectively, with corresponding estimates of maternal heritabilities being 0.14, 0.21 and 0.42. Genetic correlations between direct and maternal effects (r_am) were negative for all three traits, varying from -0.40 to -0.65. Maternal permanent environmental effects were 0.06, 0.12 and 0.11 for BW, WW and CE, respectively. Direct breeding values and maternal breeding values for BW and WW decreased with increasing proportion of Hereford. Direct breeding value for CE increased, while maternal breeding value for CE reached a minimum value at 0.62 proportion of Hereford.