Reading RGz 9ATThe purpose of rearing calves is that they should reproduce, lactate and produce meat for human consumption. T h e problems associated with achieving these aims are twofold; first, that the most economic system of rearing should be used and secondly, that the quality of the diet should fulfil the nutritional requirements of the calf and maintain its health.
MortalityPerinatal mortality (stillbirths and deaths within 12-24 h of birth) is about 3% and tends to be higher for breeds of extreme size. For large breeds perinatal mortality is associated with difficulties at parturition caused by a disproportionate increase in size of the calf relative to that of the dam (Monteiro, 1969) whereas for small breeds it tends to be associated with weak calves, which would appear to have suffered nutritional deficiencies in utero.Postnatal mortality during the first 4 weeks is also about 3%, mainly associated with enteric infections and representing about 60% of the mortality to 26 weeks of age.Systems of rearing Growth rate. T h e growth rate of calves during the first 3 months of life is positively related, between breeds, to birth weight and can vary, according to the plane of nutrition, up to a maximum of about 1-5 kg/d. Although with a moderately high plane of nutrition (0-95 kg/d) first oestrus and conception may occur in Friesians at about 6 months of age, there is a wide variation among animals. I n commercial practice, conception is not planned to occur before 15 months at the earliest, and often not until about 27 months of age, with over-all growth rates of about 0.70 and 0.45 kg/d respectively. Breeding is delayed because of the fear of difficulties at parturition and of reduced milk yields and longevity, or because the producer does not have the nutritional knowledge to achieve the desired growth rates, or considers them to be uneconomic.