Measuring spatial and temporal variation in lactating dairy cow placement on diverse grazing system farms

Abstract The locations dairy cows visit on grazing system farms can have important implications for nutrient management. Excreted nutrients can be directly returned to pasture paddocks, or returned to places where these nutrients can either be collected for reuse, or are not collectable and therefore lost. Previous research has shown that nutrient accumulation was related to the time cows spend in places on farms, but there is little literature describing the spatial or temporal variation in the locations lactating dairy cows visit on grazing system farms. We developed a methodology to quantify the time lactating cows spend in different places on 43 representative grazing system farms to better understand the potential for excreta deposition and collection. These farms were diverse, with the herds visiting a wide variety of places where they spent differing lengths of time. The lactating dairy herds spent the majority of their time on pasture paddocks (74.2%; 0 to 97.6%), and only 10% (1 to 25%) of their time in locations where nutrients are routinely collected for storage and re-use, (i.e. the dairy shed (milking parlour) and associated yards). However, the paddocks where the cows were placed were not uniformly distributed around the farm, with significantly more time spent in paddocks overnight, that were located an average of 118 m closer to the dairy shed than paddocks the cows visited during the day. Feedpads and holding areas were the other places on farms that cows often visited, and where they spent 9.5% and 18.2% of their time respectively. However, only half of the feedpads in this study were concreted to facilitate collection of excreted nutrients for redistribution. Using excretion rates from the literature and data collected in this study, an estimated 1.0, 7.3 and 5.1 t of P, N and K respectively would be deposited within 100 m of the dairy shed by a 326 cow herd over a 300 day lactation on a grazed dairy farm. Up to 50% of the nutrients deposited near the dairy shed are potentially not collected and recycled. These results suggest that quantifying animal numbers and the time they spend in various locations are essential to determine nutrient deposition within dairy grazing systems and to improve farm nutrient use efficiencies.