33The economic effects of early-life nutritional constraints in crossbred cattle bred on the NSW North Coast

Executive Summary

Modern Australian beef cattle husbandry practices aim to grow cattle efficiently on pasture during the early phases of their lives, followed by the use of high quality feedstuffs during later growth phases to reduce the risk of not meeting the targeted premium market specifications. However, pasture-reliant growth of cattle is typically a prolonged process during which cattle experience widely differing nutrition levels and growth paths due to variable pasture quality and availability, climatic extremes, and constraints on management of cattle and pastures. Different patterns of nutrition during pregnancy and lactation can influence cow productivity and the performance of their offspring. This issue has assumed greater importance in recent times with the ongoing drought and the prospect of even greater variability in climate due to global warming.

An experiment was conducted on the North Coast of NSW whereby “low” and “high” pasture nutritional systems were imposed on a herd of Hereford cows during pregnancy, and then again from birth to weaning, with a crossover design also imposed to select offspring with extremes of growth to birth and/or weaning. Thus, four nutritional cow and offspring growth groups resulted – low-low, low-high, high-low, and high-high. The aim was to maximise the divergence, within animal welfare limitations, in foetal and pre-weaning growth of the progeny, and to investigate the subsequent differences in growth rates and carcass characteristics of offspring through to market weights. To cover the range of market specifications, both Piedmontese (high muscle growth and high birth weight) and Wagyu (high marbling and low birth weight) bulls were used. The progeny of the experiment were grown out or backgrounded on the NSW Northern Tablelands until about 26 months of age then finished in a feedlot for around 120 days.

The results of the experiment indicated that restricted early-life growth resulting in differences in weight of calves at weaning persisted until slaughter at 30 months of age. Animals that were smaller at weaning remained smaller at slaughter. Some compensation occurred following restriction of growth during lactation, but not following restriction of growth during pregnancy. However, neither carcass quality nor eating quality of the beef was adversely affected by growth restriction during early-life.

An economic analysis of these data was done using the Beef-N-Omics decision support package. Two different methods were used to test whether following the experimental protocols (different weights at feedlot entry) resulted in economic outcomes different from those resulting from applying typical commercial practice. The first (following the protocols) showed that for the representative cattle enterprise modelled, total gross margins ranged from $45,500 for the low-low system to $52,600 for the high-low system. Gross margin per hectare ranged from $114 for the low-low system to $132 for the high-low system, while gross margin per breeding cow ranged from $303 for the low-low system to $387 for the high-high system. The second method (adjusting for a common feedlot entry weight) showed slightly lower gross margins for each early-life treatment group, but the same ranking of groups. However, in all cases, the gross margin for those animals that commenced foetal growth on a high plane of nutrition and a high growth trajectory exceeded their peers on the low plane of nutrition and low growth trajectory.

It is more profitable for cows and calves to have access to a high standard of nutrition during pregnancy and up to weaning than for them to have access only to a poor standard of nutrition during this time period. Further, if feed is in short supply and a choice has to be made, it is more profitable for cows to have access to a high standard of nutrition during pregnancy than for cows and calves to have access to a high standard of nutrition between partuition and weaning.