Effect of Supplementation and Lactation Stage on Performance of Grazing Dairy Ewes
The dairy sheep industry in the United States has been growing over the past 25 years, with many flocks located in temperate regions well suited to pasture production. As the number of sheep dairy farms increases, so does the need for information regarding pasture based production and supplementation. The study will determine if there is a significant difference between milk production of ewes at different stages of lactation fed only pasture and ewes fed pasture with grain supplementation. The research will evaluate dairy sheep production on high quality pastures, mainly kura clover-grass mixtures. In addition, the study will evaluate differences in milk composition of supplemented and unsupplemented ewes. The study will monitor milk fat, milk protein, milk urea nitrogen (MUN), milk solids and somatic cell count of milk from supplemented and unsupplemented ewes. These milk factors affect subsequent cheese production and MUN is an indicator for protein utilization. The study will estimate dry matter intake on pasture through the use of an external marker, titanium dioxide, noting differences between treatment groups. The results of the study will directly benefit pasture based sheep dairy producers by providing information regarding protein utilization on pasture. The information this project generates will help dairy sheep producers and researchers finely tune animal nutrition requirements for profitable and sustainable flocks.
This project will evaluate the effects of supplementation and stage of lactation on milk production of dairy ewes grazing high quality pastures. The project will provide information to farmers and researchers about the need for supplementation to grazing dairy ewes for maximum production and efficient nitrogen utilization.
Expected short-term outcomes are:
1)Determine milk production from treatment groups.
2)Determine protein utilization of treatments through analysis of milk urea nitrogen levels.
3)Determine quality of kura clover and grass pastures.
4)Determine dry matter intake of grazing dairy ewes.
Intermediate-term outcomes: Dairy sheep producers will directly benefit from the information regarding milk production and protein utilization on rotationally grazed pastures. This information will emphasize the value of legume-grass pastures as the basis for a sustainable sheep dairy operation. In addition, milk composition information will be gathered from treatments of lactation stage and supplementation level. This information is valuable to dairy sheep processors and marketers promoting domestic sheep dairy producers and products.
Long-term outcomes: The results of this study will help dairy sheep producers and researchers finely tune animal nutrition requirements for profitable and sustainable flocks. Promotion of pasture-based dairying will encourage farmers to improve and monitor pastures. It will encourage the use of a rhizomatous, perennial legume, kura clover, in permanent pastures to improve soil fertility and stability. It will also promote a dialog among producer and scientific community regarding the continued improvement of forages for dairy sheep nutrition in the United States, a fledgling industry committed to rotational grazing.
The grazing trial was conducted in 2005. Milk production and composition information was gathered during the trial period. Forage samples were collected from pastures and analyzed for crude protein and neutral detergent fiber. In addition, paddock dry matter allowance was measured using a rising plate meter. Pasture information is still being related to milk production through statistic analysis. Administration of titanium dioxide boluses and collection of fecal samples was completed during the grazing season. These fecal samples are in the process of being analyzed for titanium dioxide concentration in an attempt to determine pasture dry matter intake.
Impacts and Contributions/Outcomes
Unsupplemented ewes in both lambing groups showed a greater range in their daily milk yields than supplemented ewes throughout the trial, probably in direct response to variations in pasture quality during the grazing season. The January lambing ewes compared to the April lambing ewes produced less (P < .001) milk (91.1 vs. 136.8 kg, respectively), milk fat (5.6 vs. 7.8 kg, respectively), and milk protein (4.7 vs. 6.3 kg, respectively) during the trial. The supplemented ewes compared to the unsupplemented ewes produced more (P < .01) milk (123.2 vs. 104.2 kg, respectively), milk fat (7.2 vs. 6.2 kg, respectively), and milk protein (5.9 vs. 5.0 kg, respectively). Supplementation had a similar positive effect on milk, milk fat, and milk protein yield in both lambing groups. Given the current cost of supplement and the price of sheep milk, supplementation was profitable.
Milk urea nitrogen (MUN) can be used as an indicator of the efficiency of protein utilization in sheep. Trial MUN levels across treatments tended to be higher (18 to 34 mg/dL) than recommended levels for sheep (14 to 22 mg/dL), indicating an excess of protein intake. This can be explained by the high quality pastures, which ranged in crude protein from 16 to 30 %. Since ewes were receiving adequate levels of protein from the pasture alone, a supplement with lower protein, and therefore lower cost, may have been sufficient. Across all treatments, the correlation between pasture crude protein and MUN was .65. Within the supplementation treatment, the correlation was numerically higher, but not significantly different, than the correlation within the unsupplemented treatment (r = .78 and .52, respectively).
Further laboratory analysis is being conducted to determine dry matter intake of ewes in each treatment. This will indicate if unsupplemented ewes are consuming more pasture than supplemented ewes.