Effects of protein concentration and degradability on performance, ruminal fermentation, and nitrogen metabolism in rapidly growing heifers fed high-concentrate diets from 100 to 230 kg body weight.

Abstract

Twenty crossbred heifers (101 +/- 4.5 kg BW) were used to examine the effects of protein concentration and degradability on performance, ruminal fermentation, nutrient digestion, N balance, and urinary excretion of purine derivatives. Heifers were offered concentrate and barley straw for ad libitum consumption. Two protein concentrations (17 vs 14%, DM basis) and two protein sources differing in ruminal degradability (58 vs 42% of CP for soybean meal and treated soybean meal, respectively) were tested. The experiment was divided into four consecutive 28-d periods to evaluate the age (period) effect. Increasing protein concentration and degradability did not improve ADG or intake (P > .05). The increase in urinary N excretion (P < .001) in heifers fed 17% CP suggests that N was in excess of requirements. When the low-degradable protein source was supplemented and(or) CP concentration was low, ruminal NH3 N concentrations fell below 5 mg/100 mL. Urinary excretion of purine derivatives was not affected (P > .05) by protein concentration and degradability, suggesting that in high-concentrate diets NH3 N concentration was not limiting microbial growth. Total VFA concentration decreased (P < .001) and the acetate:propionate ratio increased (P < .01) with advancing period, suggesting an increase in ruminal absorption capacity and an increase in fiber fermentation. The decrease in ruminal NH3 N concentration in the last period suggests a greater use of NH3 N by microorganisms. This hypothesis is supported by the increase (P < .001) in urinary excretion of allantoin and estimated duodenal flows of purine bases and microbial protein with advancing period. Reducing CP concentration and increasing ruminal undegradable protein supply did not affect animal performance or estimated duodenal flow of microbial protein in rapidly growing heifers fed high-concentrate diets.

Effect of feeding method on intake and behaviour of individually reared beef heifers fed a concentrate diet from 115 to 185 kg of body weight

“…However, in both treatments, heifers ate less forage than expected and much less than the level of 20% proposed by Forbes and Provenza (2000) for ruminants given a free choice between forage and concentrate. This result is in agreement with data obtained by Devant et al (2000) in young heifers (80 kg BW) given free-choice barley straw and concentrate in which they found a concentrate to forage ratio of 95 to 5, between the ratio recorded in the present experiment (96 to 4 and 94 to 6 for CH and TMR treatment, respectively). To design a TMR diet for young animals, it may be necessary to reduce the proportion of barley straw to fit the animals' requirements better.…”

“…However, young cattle fed diets based on concentrate and barley straw, offered both ad libitum and separately, consume the roughage in a much lower proportion. Devant et al (2000) reported that the concentrate : barley straw ratio decreased from 95 : 5 to 92 : 8 -E-mail: Alfred.Ferret@uab.cat in Friesian crossbred heifers from 80 to 230 kg BW. Gonzá lez et al (2008), working with Friesian heifers from 140 to 380 kg BW in feedlot conditions, reported an average concentrate : straw ratio of 89 : 11 when both ingredients were also offered separately and on an ad libitum basis.…”

Nutritional strategies to control ruminal acidosis in feedlot cattle

“…There were not differences in acetate, propionate or butyrate proportions among treatments within each trial, and acetate:propionate ratios were representative of those reported in beef cattle fed high-concentrate diets (Devant et al, 2000;Martin et al, 2010), with an average value of 1.57. However, VFA concentration significantly varied along the time following a cubic relationship ( Figure 5.5.…”

“…Cereal straw is fed ad libitum in order to maintain the rumen function and to reduce the impact of the high availability of starch (Gimeno et al, 2014), as straw promotes chewing and salivation and contributes to maintain the buffering capacity of the rumen. However, straw intake is generally low (below 12% of total DMI; Devant et al, 2000;Gimeno et al, 2014;Iraira et al, 2015), and related to the necessary quantity to maintain rumen functionality.…”

“…González et al (2008ab) conducted several trials to investigate the effects of increased social pressure caused by a reduced number of concentrate feeding places on performance and behaviour of beef cattle, and reported that reducing the feeding space (25 vs. 12.5 cm per animal) reduced animal performance, increased concentrate eating rate and reduced straw eating time during peak feeding times, which may result in lower ruminal pH. Different studies have reported straw intakes in beef cattle fed high-grain concentrates and straw on a feed-choice system ranging from 3.9 to 10.2% (Devant et al, 2000;Gimeno et al, 2014;Iraira et al, 2015). The high straw intake estimated in our study should have increased the NDF intake, which may have increased rumination and chewing and contributing to mask the possible differences in corn and wheat fermentation.…”