Protein supplementation of ruminants consuming low-quality cool- or warm-season forage: Differences in intake and digestibility

Abstract

An in situ study (Exp. 1) using 4 ruminally cannulated steers (343 ± 11 kg of BW) in a completely randomized design was used to compare ruminal degradation characteristics of low-quality cool-season (C3; Kentucky bluegrass straw; Poa pratensis; 6.3% CP; DM basis) and warm-season (C4; tallgrass prairie; 5.7% CP; DM basis) forage. Four ruminally cannulated steers (252 ± 8 kg of BW; Exp. 2) and 4 wethers (38 ± 1 kg of BW; Exp. 3) were used in two 2 × 2 factorial arrangements of treatments to determine the influence of supplemental CP (CPSupp; soybean meal; 0.09 and 0.19% of BW, CP basis, for steers and lambs, respectively) on nutrient intake and digestion of C3 and C4 forages. Steers and wethers were allotted to separate 4 × 4 Latin squares that ran simultaneously with 20-d periods. In Exp. 1, C3 had a greater A fraction (fraction of total pool disappearing at a rate too rapid to measure) and effective degradability of DM and NDF compared with C4 (P < 0.01). In addition, C3 had a greater (P < 0.01) A fraction and effective degradability of N, whereas the C fraction (fraction of total pool unavailable in the rumen) was less (P < 0.01) than those for C4. Consequently, RDP accounted for 84.7% of total CP in C3 as compared with 66% for C4 (P < 0.01). In Exp. 2, a CPSupp × forage interaction (P < 0.01) was noted for forage and total DMI, with CPSupp increasing intake of C4 by 47% and intake of C3 forage by only 7%. Dry matter digestibility responded similarly, with a CPSupp × forage interaction (P = 0.05; CPSupp increased digestibility by 21% with C4 and by 9% with C3 forage). In addition, CPSupp × forage interactions were noted for ruminal liquid retention time (P = 0.02; CPSupp decreased retention by 3.6 h with C4 and by only 0.6 h with C3 forage) and particulate passage rate (P = 0.02; CPSupp increased passage by 46% with C4 and by 10% with C3 forage). As in Exp. 2, a CPSupp × forage interaction (P = 0.01; CPSupp increased digestibility by 18% with C4 and by 7% with C3 forage) was observed with DM digestibility in Exp. 3. In contrast, only N balance (P < 0.01) and N digestibility (P < 0.01) were affected by CPSupp. These data suggest that intake and digestion of low-quality C3 and C4 forages by ruminants are not similar and, more important, that the physiological response of ruminants to protein supplementation of low-quality forage is dependent on forage type.

Protein requirements for growth in male and female Saanen goats

“…This value may appear inconsistent; however, other reports in the literature present similar (Ghassemi Nejad et al, 2014) or even greater values than ours for other small ruminants (Kiran and Mutsvangwa, 2007), raising the hypothesis that the excretion of nitrogen is dependent on metabolic processes through which balance is achieved in response to a dietary change (Waterlow, 1999). Indeed, Bohnert et al (2011) reported a variation of N excreted in urine of 400% depending on dietary manipulation.…”

“…The literature has reported variations in nitrogen excretion in feces (Blaxter and Mitchell, 1948;Lobley et al, 2000;Kiran and Mutsvangwa, 2007;Huhtanen et al, 2009;Dias et al, 2011) and urine (Kiran and Mutsvangwa, 2007;Bohnert et al, 2011;Ghassemi Nejad et al, 2014) due to dietary changes and environmental conditions. The circumstances causing this phenomenon are poorly understood (O'Brien et al, 2010;Bernabucci et al, 2010;Mahjoubi et al, 2014).…”

“…However, this relationship is hard to ensure given the wide range of feeds and by-products that are used in animal nutrition; even traditional feed may change between temperate and tropical conditions. It must also be considered that the difference among roughages around the world is enormous (Robinson et al, 2006;Bohnert et al, 2011) and may vary in fiber characteristics and content. Fiber characteristics are very important in this context; for example, tropical feedstuffs, because of a greater content of ADF, can increase undigested N (NIDA) in feces (Bohnert et al, 2011).…”

“…It must also be considered that the difference among roughages around the world is enormous (Robinson et al, 2006;Bohnert et al, 2011) and may vary in fiber characteristics and content. Fiber characteristics are very important in this context; for example, tropical feedstuffs, because of a greater content of ADF, can increase undigested N (NIDA) in feces (Bohnert et al, 2011). In addition, Tamminga et al (1995) suggested that the presence of more fibrous feed in the diet may increase the endogenous N in feces due to saliva, digestive enzymes, and increased bile secretion, and the sloughing of intestinal mucosal cells and mucins in response to the diet.…”

Substitution of rumen degradable nitrogen with urea in sheep fed low quality Eragrostis curvula hay

“…A possible reason for the inconsistent results observed in supplementation studies is the differences in nutrient bioavailability between low quality tropical and temperate forages (Bohnert et al, 2011). Low quality temperate grasses contain higher levels of water soluble carbohydrates (WSC) and RDN levels compared to tropical grasses (Bohnert et al, 2011).…”