Farm Table says:
What is the problem?
A large variation in live weight gain (LWG) exists in cattle grazing crude protein (CP) deficient pastures after weaning across northern Australia. This occurs even when N supplements are provided.
The research design was to:
- Assess relationships between insulin-like growth factor-1 and metabolites associated with growth and nutrient status of animals and post-weaning live weight gain of cattle grazing low and high crude protein pastures.
- A better understanding of the reasons for the divergence in post-weaning live weight gain which exists in northern Australian cattle herds.
What did the research involve?
- Experimental design and animals
The experiment was conducted in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes and was approved by the Charles Darwin University and University of Queensland Animal Ethics Committees.
Beckman Coulter Diagnostic Systems kits. Insulin-like growth factor-1 concentration in serum was determined using the Bioclone IGF-1 radioimmunoassay kit according to the manufacturer’s instructions (Bioclone; NSW, Australia), with radioactivity counted on a Perkin Elmer 2470 gamma counter
- Statistical analysis
Change in live weight and HH during each of the three phases of the experiment was determined by linear regression.
What were the key findings?
- Average daily LWG of steers in the entire mob over this period was 0.12 0.01 kg/d (ranging from -0.22 to 0.44 kg/d).
- Between the end of Phase 1 and the commencement of Phase 2, there was no change in live weight of L-ADG steers (147.8 vs. 147.3 kg, respectively) however, H-ADG steers lost live weight (163 vs. 155.2 kg, respectively) over the three week period.
- There was a positive correlation between live weight and HH of steers at the end of the wet season grazing period (r=0.63; P<0.001).
- The results confirm that within a mob, Bos indicus weaner growth rates in commercial beef herds in northern Australia may be highly variable. This variability does not appear to be related to the nutrient status of the animals, as there were no differences in plasma albumin, creatinine, glucose or urea concentrations between the fastest and slowest growing steers at weaning or 91 days later.
- Steers that grew at higher (0.21 kg/d) and lower (0.03 kg/d) growth rates over the 91 day period after weaning, grew at similar rates when fed a higher protein cavalcade hay (0.47 kg/d) or moderate protein Mekong grass-based diet (0.28 kg/d) in pens.
- Serum concentration of albumin, creatinine, glucose and urea and the U:C did not differ between LADG and H-ADG steers, either at weaning or 91 days post-weaning.
- Insulin-like growth factor-1 concentration did not differ between animals that were divergent in LWG during the post-weaning period, at any stage of the experiment, which is in contrast to the findings of Turnbull (pers. comm.).
- The result of Turnbull was based on a single sample collected 100 days after weaning and on a small number of animals only, which may account for the different findings between the experiments.
The logic for the divergence in live weight gain post-weaning is likely to be related to variability in responses to marking and weaning grazing behavior or supplement intake rather than genetics or health status.