Summary
Cattle in extensive systems are often subject to periods of reduced feed availability due to the normal seasonal cycles in pasture growth or more extreme conditions, such as drought. When nutrient intake fails to meet metabolic requirements in the animal, an adaptive response is initiated resulting in catabolism of fat and muscle tissue and subsequent reductions in liveweight and body condition.
During prolonged periods of under-nutrition, the losses in body mass can be quite significant and this in turn, negatively affects productivity (eg reduced reproductive function). Whilst the productivity losses have been characterised, very little is known about the impacts on animal welfare during moderate and sustained under-nutrition in livestock. Body condition score (BCS) has been used as a practical and effective means to monitor changes in body mass and composition in cattle on-farm. It potentially may also provide an indication of welfare status. In order to use BCS as a scientifically defensible measure of animal welfare, there is a need to firstly, determine the welfare state of animals differing in BCS and secondly, to identify the key thresholds of these measures in terms of acceptable and at-risk animal welfare.
The primary objective of this joint Australian and New Zealand project was to determine whether BCS could be applied as a practical measure of welfare in cattle during periods of moderate under-nutrition. A secondary objective was to identify the minimum BCS and maximum rate of change in BCS and live weight for application within industry welfare standards and/or assurance systems. The class of animal targeted in the research was the lactating beef cow since she is likely to experience the largest fluctuations in BCS during each pregnancy/lactation cycle. In New Zealand, the focus was the gestational ewe and this joint research formed part of the Animal Welfare Objective Measures (AWOM) Research Program.
Three cattle experiments were conducted in this project. The aim of the first experiment was to validate a methodology to objectively quantify an animal's motivation for food and therefore provide an indication of hunger. The second experiment evaluated the behavioural and physiological responses in lactating cows differing in fat score (FS). In the third and final experiment, the behavioural and physiological responses in lactating beef cows were examined in response to different rates of condition loss and at stable differences in BCS.
The primary conclusions from the research were:
Fat scores, based on estimates/measurements of subcutaneous fat, are inadequate in the determination of body condition, or more specifically, condition loss in lactating beef cows. A more appropriate alternative is body condition scoring which is based on both visual and manual assessments of the flesh (muscle + fat) covering the skeleton. However, currently there is no national standard for body condition scoring in beef cattle. It is therefore recommended that if body condition score is to be used as an indicator of the welfare status in cattle, there is a need to develop a national standard system that is appropriate for Australian beef cattle breeds and classes. Alternatively, given that the AUS-MEAT Fat Score System is nationally recognised, examine whether the system can be modified or augmented to better reflect both fat and muscle loss particularly around the at welfare risk category of FS 1.
Assessments of BCS were moderately to highly correlated with objective indicators of fatness and muscle mass (ie. body composition). Similarly, BCS was moderately associated with endocrinal regulators of appetite and energy homeostasis (eg. leptin). These results add to the evidence that BCS can be a reliable and practical indicator of body composition and can be applied to monitor cattle when they are in catabolic states.
In Experiment 2, a significant difference in feeding motivation was found between FS1-1.5 cows and the combined FS 2 and FS 3 cows but the differences between BCS treatment groups in experiment 3 were not significant. Nevertheless, there was a similar trend to that observed in the second experiment where the low condition score cows showed higher motivation for food than the higher condition score groups. This aligns with the findings of the complementary sheep BCS research undertaken as part of the AWOM Research Program. Collectively, these data provide the first quantitative evidence of the relative hunger experienced by ruminants during under-nutrition. Although there were inconsistencies in the cattle results, there is sufficient evidence to suggest that BCS can be applied to assess the welfare of ruminants during moderate under-nutrition. However, since this is the first attempt to explore the impact of condition loss in the context of hunger and animal welfare in cattle, further research is warranted.
Whilst BCS appears to provide an indication of welfare status in lactating cows during moderate and sustained under-nutrition, the actual BCS threshold that delineates acceptable and unacceptable welfare is much harder, and perhaps impossible to define. Alternatively, we propose that it is more appropriate to consider BCS in the context of welfare risk where there is an optimal BCS range and outside this, the welfare risks increase with either increasing or decreasing BCS. Industry guidelines recommend the optimal BCS range for heifers and cows at the time of joining and calving is 2.5 - 3.5 (1-5 BCS scale). This is largely predicated on maximising reproduction performance but it has relevance in terms of animal welfare. Based on the present research, at a BCS < 2.5 there appears to be an increased risk that cows will experience hunger. It must be emphasised that a cow with BCS outside the optimal range does not automatically have compromised welfare, rather it provides an indication that she may be at risk of an adverse welfare outcome.
It is recommended that regular assessments of BCS are central to the effective management of welfare risks during periods of drought or reduced pasture availability in beef herds.
