Partial substitution of maize with soybean hulls in a concentrate supplement for grazing dairy cows

[摘要] ENGLISH ABSTRACT: Climate in the southern Cape region of South Africa permits dairy farmers to make use of cultivated pasture as their main nutrient and feed source for dairy cows. A commonly used pasture system in this region is kikuyu over-sown with ryegrass. Pasture has a limited supply of nutrients which necessitates the need to provide dietary supplementation in a concentrated form. Concentrates consists primarily of maize grain which is a highly priced product containing a high starch content. Including alternative feed ingredients with lower starch content, higher level of digestible fibre and possibly a lower cost in concentrates may improve milk production and milk composition. Soybean hulls are one of many by-products which are considered as an alternative to maize. The hulls are a by-product after processing of soybeans for oil and meal, and are high in energy, crude protein (CP) and fibre which make it a possible alternative to maize in dairy feed as it is digested more efficiently by ruminants. The aim of this study was to determine the effect of partial substitution of a maize in a dairy concentrate with soybean hulls, on milk production, milk composition, digestion of kikuyu-ryegrass pasture and rumen environment.Fifty-one lactating Jersey cows from Outeniqua Research Farm were blocked according to mean milk yield, days in milk (DIM) and lactation number for the production study. Cows used were between 127 ± 50.5 DIM. A complete randomised block design was used. Cows within each block were randomly allocated to one of the three treatments. Treatments were defined according to the level of soybean hulls included in the concentrate supplement: SH0, SH15 or SH30 containing respectively 0%, 15% or 30% soybean hulls. Cows were fed 6 kg/day (3 kg per milking session) concentrates. After each milking session the cows grazed fresh kikuyu-ryegrass pasture allocated at ± 13 kg dry matter (DM)/cow per day. There were no significant differences (P > 0.05) in milk yield, 4% fat corrected milk (FCM) and energy corrected milk (ECM) between treatments. Milk fat tended (P = 0.06) to increase when 15% soybean hulls were included. Milk protein and lactose percentages increased significantly (P < 0.05) when soybean hulls were included (15 and 30%) in the concentrates. Somatic cell count (SCC) did not differ significantly between treatments. The milk urea nitrogen (MUN) content (8.30 – 9.36 mg/dL) indicated that sufficient protein was supplied to cows on all treatments. Cows on all three treatments gained weight and improved in condition during the study. Live weight of cows did not differ between treatments. Body condition improved (P < 0.05) when 15% soybean hulls were included indicating sufficient energy supply.Nine ruminally cannulated cows from the Outeniqua Research Farm were used for the rumen study. A 3 x 3 Latin square design was used, where all cows were subjected to all three treatments. In each period, cows were randomly allocated to one of the three treatments. Cows were fed 6 kg/day (3 kg per milking session) concentrates. After each milking session the cows grazed together with the production study cows on fresh kikuyu-ryegrass pasture allocated at ± 13 kg DM/cow per day. There were no significant differences in the rumen pH among treatments. Acetate production showed no significant difference among treatments. Rumen propionate and butyrate concentration was lower (P ≤ 0.05) when 30% soybean hulls were included compared to the control. The ratio of acetate to propionate increased (P < 0.05) when soybean hulls were included at 15 and 30%. Rumen ammonia nitrogen (NH3-N) increased (P < 0.05) when 30% soybean hulls were included. After 30 h of incubation the in sacco DM disappearance of ryegrass pasture was higher (P = 0.05) when soybean hulls were included. The in sacco neutral detergent fibre (NDF) disappearance of kikuyu-ryegrass pasture after 30 h of incubation increased significantly when 15% soybean hulls were included, compared to 0% soybean hulls.The study showed that milk production can be maintained when as much as 30% soybean hulls replaced maize in the concentrate. Replacing 15% of the maize tended to increase milk fat content and increased milk protein and lactose content significantly.

[发布机构] Stellenbosch University