Abstract
Simple SummaryQuality supplementation of roughage-based cattle diets is recommended to improve the animals’ production in tropical regions. We tested the effects of two widely suggested high-quality low-cost feed supplements on feed intake, nutrient utilization and enteric methane emissions of growing female cattle. While free access to urea-molasses blocks did not effectively improve the key variables, sweet potato vine silage, a by-product of sweet potato cultivation, improved diet digestibility as well as the animals’ retention of nitrogen and lowered their methane emissions per unit of digested feed. Supplementing productive cattle with sweet potato vine silage can thus concomitantly contribute to better animal performance and lower environmental impact. Given their high nitrogen (N) concentration and low costs, sweet potato vine silage (SPVS) and urea-molasses blocks (UMB) are recommended supplements for tropical regions; therefore, they were investigated in this study. Six heifers were allocated to three diets: the roughage diet (R) consisted of wheat straw (0.61) and Rhodes grass hay (0.39; on dry matter (DM) basis); R + SPVS combined R (0.81) and SPVS (0.19); and with R + UMB animals had access to UMB. During two experimental periods, feed intake, feces and urine excretion, digesta passage, and rumen microbial protein synthesis were determined during seven days and methane emissions during three days. There was no treatment effect (p > 0.05) on DM and N intake. Apparent DM digestibility of R + SPVS (510 g/kg) was higher (p < 0.05) than of R (474 g/kg). Digesta passage and duodenal microbial N flow were similar for all diets (p > 0.05), while N retention was highest with R + SPVS (p > 0.05). Methane emissions per unit of digested feed (g CH4/kg dDM) were lower (p < 0.05) for R + SPVS (55.2) than for R (64.7). Hence, SPVS supplementation to poor–quality roughage has the potential to increase diet digestibility and N retention while reducing CH4 emissions.
Highlights
Smallholder mixed crop–livestock systems provide livelihoods for a billion people and produce a third of global beef and milk [1]
Content, whereas sweet potato vine silage (SPVS) and urea-molasses blocks (UMB) were low in neutral detergent fiber (NDF) and acid detergent fiber (ADF) and high in crude protein (CP) (Table 1)
Even though for all nutrients highest intake values (g/kg0.75 live weight (LW)) were determined for R + SPVS, there was no effect of diet on the quantitative intake of dry matter (DM), organic matter (OM), NDF, ADF, and CP (Table 2)
Summary
Smallholder mixed crop–livestock systems provide livelihoods for a billion people and produce a third of global beef and milk [1]. Ruminants in mixed systems are often provided with poor-quality forages or crop residues [2], which supply insufficient energy and nutrients [3,4]. This results in low performance [5], live weight (LW) losses [6,7] and a negative nitrogen (N) balance [6,8]. Piñeiro-Vázquez et al [12] were able to lower
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