Effects of Brewery Byproducts on Dairy Cows in Northern Tanzania

An on-farm monitoring experiment was conducted to assess the effect of supplementing lactating dairy cows with wet spent grain by-products (WSGB) on milk production, methane emissions, and economic profitability in smallholder dairy systems in Northern Tanzania. Forty (40) lactating cross-bred dairy cows, with equal numbers selected from two locations: Arusha City Council (ARCC) and Hai District Council (HDC) were subjected to two dietary supplements, wet spent grain by-products (S1) and common concentrates (S2) in a 2x2 factorial arrangement. Data on feed intake, milk yield, milk composition and methane emissions were recorded for a period of 30 days, including 7 days of adaptation. An economic analysis was performed to evaluate the profitability of the two supplements in the study areas. Body weights (BW) were estimated using heart girth width measured using weighing bands. Near-Infrared spectroscopy (NIRS), lactoscope 300<sup>MT</sup>, and laser methane detector (LMD) were employed to determine the chemical composition of the feedstuffs, milk quality and methane (CH<sub>4</sub>) emissions from the cows, respectively. The results showed that the average values (%) of crude protein (CP) and neutral detergent fibre (NDF) of supplement S1(21.93 and 53.35, respectively) were higher (P<0.05) than those of S2(12.63 and 29.12, respectively). The mean values of intake (g/kg BW) of CP and supplement NDF were higher (P<0.05) in cows supplemented with S1(3.23 and 3.06, respectively) than those on S2(2.48 and 1.04, respectively). Similarly, cows supplemented with S1 had higher (P<0.05) average yields of milk (39.7 g/kgBW), milk fat (308 g/kg of milk) and milk protein (449 g/kg of milk) than those on S2(33.64, 201.96, and 358.25, respectively). The gross margin (TZSH, per litre of milk) was higher (P<0.05) for cows fed on supplement S1 (777.38) than those on S2(622.48). In terms of location, cows in ARCC had a greater gross margin (701.08) than those in the HDC (698.8). The amount of methane (g/litre of milk) emitted from the cows on S1(11.7) was lower (P<0.05) than their counterparts in S2 (17.2), and the intensity was more pronounced in ARCC (17.27) compared to HDC (11.54). It is concluded that wet spent grain byproduct is a valuable supplement for dairy cows, effectively enhancing milk yield, gross margin from milk sales and lowering methane emissions. Further investigation is recommended into the optimal level of combination of brewery by-products with common concentrates to optimize nutrition and production potential of the cows.