Effect of dietary forage: concentrate ratio on the behaviour, rumen fermentation and circulating concentrations of IGF-1, insulin, glucagon and metabolites of beef steers and their potential effects on carcass composition

Abstract

In an investigation of factors responsible for the lower efficiency of carcass lean gain seen previously in steers offered grass silage diets 18 Simmental × British Friesian steers (361 (s.e. 5-35) kg) were offered one of three diets: a perennial ryegrass silage ad libitum and alone (S) or supplemented with rolled barley at 300 g/kg of total dry matter (SC) or supplemented as described but restricted (SCr) in quantity so as to provide the same dry matter (DM) and digestible energy (DE) intakes as for S. Eating (Eb), ruminating (Rb), standing (Sb) or lying (Lb) behaviour was quantified during four 24-h periods of manual observation. Eb was noted in more detail in a second experiment using computerized Calan-Broadbent gates and load cells to monitor times and rates of eating. Blood was taken via temporary indwelling jugular catheters at 30 to 60 min intervals on each of 4 days 1 month apart. Rumen fluid was sampled hourly for three 24-h periods from three rumen-cannulated steers given the same three diets in a separate 3 x 3 change-over design experiment.Steers offered the restricted diet SCr ate most of their food in one extended meal within 6 h of feeding while two peak eating periods (morning and evening) were observed in steers offered the other two diets. Steers offered SCr spent more time in Sb (P < 0.05), and less time in Eb (P < 0·001) and Rb (P < 0·05) activities than did animals offered the two diets ad libitum (SC and S). Mean 24 h insulin-like growth factor-1 (IGF-1) concentrations and postprandial insulin concentrations were significantly higher with diet SCr than with diet S (P < 0·001) despite equal daily DM and DE intakes from each. Insulin appearance in the jugular vein reflected the pattern of food intake on all treatments. Rumen fermentation characteristics were largely unaffected by diet. Mean 24 h rumen volatile fatty acid, pH and ammonia concentrations did not differ between diets but post-prandial rumen pH tended to be lower in animals offered the SC and SCr diets.Differences in patterns of food intake between animals offered food ad libitum and at a restricted level are likely to determine patterns of nutrient absorption and the secretion of nutritionally regulated splanchnic hormones. The higher proportions of Sb and Rb activities in steers offered the restricted diet represent an energy cost to these animals while the higher plasma IGF-1 and insulin concentrations also seen in these animals may collectively influence the partitioning of nutrients to the peripheral tissues and contribute to the increased efficiency of carcass lean deposition previously shown in animals offered such diets.

Evaluation of estimated genetic merit for carcass weight in beef cattle: Blood metabolites, carcass measurements, carcass composition and selected non-carcass components

“…The lower glucose and βHB concentrations of animals on silage only is in agreement with previous findings (Thorp et al, 1999;Cummins, 2008) and can be attributed to the lower DMI of these animals (Campion et al, 2009). The higher glucose concentration of animals on the higher feeding level is also consistent with previous reports (Ellenberger et al, 1989;Reynolds et al, 2003), while the higher urea concentration in animals on silage only can be attributed to the relative imbalance between rumen degradable nitrogen and fermentable energy on grass silage diets, leading to accumulation of rumen ammonia, and ultimately urea (Thorp et al, 1999). The lower urea concentration of the dairy strains compared to the beef breeds during the first winter and at slaughter is in agreement with the findings of Clinquart et al (1995) who compared purebred Belgian Blue and Holstein bulls.…”

Effects of grazing on deposition of chemical body components, energy retention and plasma hormones in steers

“…It is likely that the lower plasma IGF‐1 levels in the grazing steers were related to the difference in dietary energy source. Thorp et al . (1999) reported that plasma IGF‐1 concentrations were lower in steers fed grass silage alone, than in steers fed a barley supplement, even though the steers in both groups had the same digestible energy intake levels.…”

High Salt Inclusion Reduces Concentrate Intake Without Major Effects on Renal Function in Young Bulls

“…Consequently, the Control bulls spent less total time eating than the 10%NaCl bulls (15.7 vs 28.2%, respectively; standard error=1.67, P<0.001). This difference could most likely be related to the lower fibre content of their diet (Thorp et al, 1999). Similarly, bulls eating a concentrate-based ration (forage-to-concentrate ratio of 8:92) spent less time eating than bulls eating a hay-concentrate diet (forage-to-concentrate ratio of 44:56) (Mialon et al, 2008).…”