Adjustment factors for weaning weights of Mashona cattle in Zimbabwe

Abstract

S U M M A R YThe effects of year of birth, age of dam, sex of calf, month of birth and weaning age on weaning weights of Mashona calves on six commercial farms in Zimbabwe were estimated by least squares procedures from data of 6365 calves born 1977-85. The least squares mean weight at 205 days among farms ranged from 123 to 159 kg while the linear regression coefficients of weight on age ranged from 0-31 to 046 kg. Adjustment for weaning age by the average daily gain from birth to weaning failed to remove the dependence of adjusted weight on age. Sex was the most important source of variation and the mean difference between male and female calves was 12-9 kg. Sex difference was markedly influenced by herd production rate, being greater in herds of above average production.Weights of calves of 3-, 4-and > 11-year-old dams deviated from those of dams aged 5-10 years (mature) by 14-5, 85 and 2-9 kg, respectively. Herd mean influenced the difference between 3-year-old and mature dams, the difference increasing as herd mean declined. Herd-year specific factors seem more appropriate for sex and 3-year-old dams and an annual crop of > 50 calves would confer an advantage to herd-specific over general adjustment factors. On the basis of equality of variances within subclasses, multiplicative factors were superior to additive factors for sex of calf and month of birth; both types of adjustment were suitable for age of dam. calf> a g e o f d a m a n d a g e o f c a l f a t w e a n i n g -T h e procedures for adjustment originated from the beef Performance recording of beef herds in Zimbabwe cattle performance recording recommendations of the was started in the 1960s and farmers are encouraged United States Beef Improvement Federation (1972). to participate in the Beef Performance Testing SchemeThe applicability of these US-based adjustment (BPTS). In essence, the scheme involves collection by factors to Zimbabwean conditions and to the smaller the farmer of cow and calf records which are then indigenous Mashona needs to be established, although processed by the Department of Agricultural Techmultiplicative factors should remove most of the nical and Extension Services to provide the farmer variation due to scale. Not only is it necessary to with adjusted values of calf weights at 205 days and confirm whether the present adjustment factors used 550 days of age. The former is a measure of calf in the BPTS are suitable, but it is also important to growth to weaning and is used mainly in dam selection, determine whether other factors exist that warrant while the latter is used as a criterion in selection of correction. Even though most farmers practise seareplacement stock.sonal breeding, with calving concentrated in SepThe Mashona is one of the three indigenous breeds tember to October before the onset of rains, a of cattle in Zimbabwe and is classified as belonging to significant proportion of calves is born outside this the Sanga type, characterized by a cervical hump. It is period. The effect of month of birth thus needs t...