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The effect of by-product inclusion and concentrate feeding level on milk production and composition, pasture dry matter intake, body weight and body condition score of mid-late lactation spring calving grazing dairy cows
There is growing interest in the use of by-products (or co-products) as economical sources of nutrients that complement grazed grass when grass supply is not sufficient to meet the nutritional demands of lactation. The objective of this research was to investigate the effect of by-product inclusion and concentrate feeding rate on milk production and composition, pasture dry matter intake (DMI), body weight (BW) and body condition score (BCS) of mid-late lactation spring calving grazing dairy cows. Forty eight (41 multiparous, 7 primiparous) Holstein Friesian dairy cows were blocked according to parity, balanced for days in milk, predicted 305 day milk yield, BCS and pre-experimental milk yield and randomly assigned to one of four dietary treatments in a 2 x 2 factorial design. All cows were grazed in one group on a perennial ryegrass based sward. The dietary treatments (T) were: concentrate containing 35% by-products offered at either 3 kg (T1) or 6 kg (T2)/ d or a concentrate containing 95% by-products offered at 3 kg (T3) or 6 kg (T4)/ d. The by-products used were maize dried distillers grains (DDG), palm kernel expeller (PKE) and soybean hulls (SH), included in equal proportions on a DM basis. The experimental diets were offered for 63 days. Pasture DMI (14.5 kg/ d) was not affected by feeding rate (P=0.37) or by-product inclusion level (P=0.27). Similarly, there were no effects of treatment on BW change (-9.3 kg, P=0.20) or BCS change (+0.07, P=0.94). By-product inclusion level had no effect on milk yield (27.33 kg/d, P=0.65) or fat and protein yield (2.00 kg/d, P=0.54). However, cows offered 6kg of concentrate produced more milk (+1.94 kg/d, P=0.08) and milk fat (+0.10 kg/d, P=0.02) than cows offered 3kg of concentrate. In conclusion, the results of this research show that by-products (DDG, PKE and SH) can be included at up to 95% of the concentrate fed to pasture based cows without impacting on milk production or composition, pasture DMI, BW or BCS. Cows offered 6kg of concentrates produced more milk and milk fat yield than cows offered 3kg, however, this response is unlikely to yield an economic return.
Keywords:
by-products, dairy cow, milk production.