Effects of incremental changes in forage: concentrate ratio on plasma hormone and metabolite concentrations and products of rumen fermentation in fattening beef steers

Abstract

As part of an investigation of factors responsible for a previously reported lower efficiency of carcass lean gain in steers offered grass silage diets, 16 Simmental × Friesian steers (515 (s.e. 6·4) kg) were offered perennial ryegrass silage ad libitum (C0) or silage plus rolled barley at 200 (C20), 400 (C40) or 600 (C60) g/kg total diet dry matter (DM). Barley-supplemented diets were intake-restricted to provide equal DM and metabolizable energy (ME) intakes to those offered C0. Eight steers were selected at random to determine the ME contents of the diets by open-circuit respiration calorimetry. The other eight steers were offered the same diets and were blood-sampled at 20- to 60-min intervals, for 10 h, to monitor changes in the concentrations of a number of nutritionally related plasma metabolites and hormones. Estimated ME intakes in these steers were 85·7, 83·1, 84·4 and 86·2 (s.e. 0·91) MJ/day from diets C0, C20, C40 and C60 respectively. Rumen-fistulated Hereford × Friesian steers provided 24-h rumen data for the same diets offered at equal amounts of ME per kg metabolic live weight.Mean 24-h plasma concentrations of insulin and insulin-like growth factor 1 (IGF-1) were linearly and positively related (P < 0·01 and P < 0·001 respectively) and glucagon quadratically related (P < 0·05) to the proportion of barley in the diet. Plasma insulin increased after feeding on all diets but concentrations on diets C40 and C60 were significantly higher than those on C0 and C20 at all post-feeding sampling times up to 9 h after feeding. Plasma IGF-1 concentrations increased above pre-feeding levels following feeding of the higher barley diets (C40 and C60; P = 0·053) but remained unchanged in steers offered C0 and C20. Mean plasma concentrations of glucose were unaffected by diet but those of β-hydroxybutyrate (BOHB) and urea were positively and negatively related respectively (both P < 0·001) to the proportion of barley in the diet. Plasma BOHB and urea concentrations also changed with time after feeding (P < 0·001). Amongst the rumen parameters measured (pH; ammonia and volatile fatty acid concentrations and proportions) only the mean 24-h concentrations and proportions of butyrate were positively related to the proportion of barley in the diet (P = 0·051 and P < 0·05 respectively). All rumen parameters were affected by time after feeding (acetate, P < 0·01; others, P < 0·001) but there was no interaction between treatment and time for any parameter.

Digestion, rumen fermentation and circulating concentrations of insulin, growth hormone and IGF-1 in steers fed diets based on different proportions of maize silage and grass silage

“…Mechanisms that control the deposition of lean and fat include the pancreatic hormones (insulin and glucagon) and the hormones of the somatotrophic axis (GH and IGF-1). Thorp et al (2000) investigated the effects of forage-to-concentrate ratio, fed as equal digestible energies, on the circulating concentrations of insulin, IGF-1, glucagon and blood metabolites in growing beef steers. They reported increases in insulin and IGF-1 concentrations in addition to increases in plasma concentrations of the metabolites b-hydroxybutyrate and urea with increasing concentrate-to-forage ratio.…”

Feeding frequency has diet-dependent effects on plasma hormone concentrations but does not affect oocyte quality in dairy heifers fed fibre- or starch-based diets

“…Thus in the present experiment (380 g starch/kg dietary dry matter (DM)) and in Sutton et al (1988) (380 g starch/kg DM, estimated from ingredient composition) and Thorp et al (2000) (340 g starch/kg DM, estimated) postprandial increases in plasma insulin and glucagon were observed when diets were fed twice daily. However, increasing the number of feeds (present experiment two to four times daily; Sutton et al, 1988, two to six times daily) or reducing the proportion of starch in the diet (present experiment; Sutton et al, 1988;Thorp et al, 2000) attenuated the response. Thus it seems necessary to exceed both a threshold in the amount of starch consumed per feed and proportion of starch in the total amount of feed consumed to increase propionate concentration rapidly enough to generate post-prandial peaks in insulin and glucagon.…”

“…Smith et al (2006) have shown that post-prandial increases in plasma insulin and glucagon concentration are related specifically to propionate absorption from the rumen into the portal circulation. Propionate production in the rumen is related to starch digestion and thus the extent of increases in plasma insulin and glucagon concentration is related to the proportion of starch in the diet (Thorp et al, 2000). However, changes in peripheral insulin and glucagon concentration in response to changes in the numbers of meals fed daily have been inconsistent.…”

“…Adamiak et al, 2006), but additionally as either two or four equal meals daily to modify post-prandial fluctuations in insulin concentration. A secondary aim was to investigate the effect of changes in glucagon concentration on oocyte quality as glucagon concentration is known to respond to feeding (Bassett, 1975) and to be dependent on diet composition (Thorp et al, 2000). Heifers of low body fatness (body condition score (BCS) , 2.5) were used because such animals (Adamiak et al, 2005 and were more responsive to nutrition than those of greater fatness (BCS .…”

Effects of energy and protein restriction, followed by nutritional recovery on morphological development of the gastrointestinal tract of weaned kids1

“…Previous studies provided evidence that IGF-I stimulated the growth of rumen epithelial cells in vitro (Baldwin, 1999). Both energy (Thissen et al, 1994) and protein (Thorp et al, 2000) intakes have marked effects on plasma IGF-I concentration and IGF-I mRNA abundance in sheep (Pell et al, 1993;Hua et al, 1995), heifers (Nosbush et al, 1996), beef steers (Thorp et al, 2000), bulls (Renaville et al, 2000), and calves (Smith et al, 2002). Feed intake and nutritional status are considered to be the main factors affecting IGF-I status in mammals (Thissen et al, 1994;Ketelslegers et al, 1995).…”