The Order of Grass and Maize Silage Supplementation Modifies Milk Yield, Grazing Behavior and Nitrogen Partitioning of Lactating Dairy Cows

Simple Summary Herbage growth is reduced during autumn, causing low mass pasture with a high N content and low energy content, while decreasing milk production and increasing urine N (N) excretion. The order of silage supplementation has been suggested as a strategy to improve intake, milk production and reduce urine N excretion, in response to changes in grazing behavior and nutrient intake produced by supplements. This study evaluates the effects of offering grass silage (GS) or maize silage (MS) in the morning or afternoon on milk yield, grazing behavior and N partitioning in lactating dairy cows. We found that time of MS and GS allocation did not modify dry matter intake, however, milk production and urine N excretion was greater for cows receiving MS in the morning and GS in the afternoon compared with cows receiving MS and GS in the morning and afternoon. Results suggest that profitability (high milk production) goes against the environmental goals (low N excretion) under the conditions of the current experiment. Abstract The aim of this study was to evaluate the effects of the order of grass silage (GS) and maize silage (MS) supplementation on milk yield, grazing behavior and nitrogen (N) partitioning of lactating dairy cows during autumn. Thirty-six Holstein-Friesian dairy cows were randomly assigned to one of three treatments, and cows remained on these treatments for a 62 days period: (1) MIX; cows supplemented with 3 kg of dry matter (DM) of silage containing 1.5 kg DM of MS and 1.5 kg DM of GS in both the morning and afternoon; (2) GS-MS; cows supplemented with 3 kg DM of GS in the morning and 3 kg DM of MS in the afternoon; (3) MS-GS; cows supplemented with 3 kg DM of MS in the morning and 3 kg DM of GS in the afternoon. All cows received a pasture allowance of 17 kg DM/cow/d and 3 kg DM of concentrate. Grazing time and pasture intake were unaffected by treatment; however, milk production was greater for MS-GS, while milk protein was greater for GS-MS. Urinary N excretion was greater for MS-GS than MIX. In conclusion, MS-GS resulted in high milk yield but also high urinary N excretion, while MIX resulted in low urinary N excretion but also decreased milk yield.