Abstract
Undernutrition of cows grazing semi-arid range as a result of drought or heavy stocking rates reduces prenatal and pre-weaning growth of their ca lves. A mechanistic model has been developed that simulates the productivity of vegetation and cattle on semi-arid savanna rangeland in southern Africa. When cows are stocked at 0.200 cows/ha instead of 0.123 cows/ha the model predicted that empty body weights of their progeny at birth and weaning would be reduced by 2.9 and 43.8 kg, respectively. If all young ani mals are stocked at 0.22 animals/ha after weaning, diffe rences in empty body weight at weaning are predicte d to persist almost unchanged for a further two years. T he model also predicted that undernutrition of catt le aged 21 months would be followed by partial compensatory growth. Comparison of simulated results with data from experiments in Zimbabwe indicates that the model realistically simulates the effects of stocking rate on cattle growth.
Highlights
Cattle grazing semi-arid range may be subjected to low intakes of metabolisable energy and protein as a result of drought, high stocking rates, or during the dry season low digestibility and low protein content of the forage (Butterworth, 1984)
In this paper a mechanistic model of a rangeland production system has been used to explain the different responses to retardation of growth that have been recorded in the literature
Model predictions of cow and calf live weights were closer to the observed values if the stocking rate of 0.200 cows/ha was used
Summary
Cattle grazing semi-arid range may be subjected to low intakes of metabolisable energy and protein as a result of drought, high stocking rates, or during the dry season low digestibility and low protein content of the forage (Butterworth, 1984). Severe chronic undernutrition of cattle in early life reduces growth and leads to smaller animals at any age (Morgan, 1972; Greenwood & Café, 2007). Undernutrition of breeding cows during the last trimester of gestation leads to a reduction in birth weight (Richardson et al, 1979) and in the cow’s milk yield (Richardson et al, 1977) as a result of the effect of undernutrition on udder development (Mellor & Murray, 1985) so that pre-weaning growth is reduced. Ainslie (1958) reported that when steers were subjected to different planes of nutrition between weaning at 8 - 9 months of age and 12 months the difference of 23 kg between group means was eliminated when all animals grazed together without being given any supplementary food. In this paper a mechanistic model of a rangeland production system has been used to explain the different responses to retardation of growth that have been recorded in the literature
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