Browsing by Subject "fertilitet"

In the beginning of lactation, dairy cows experience a negative energy balance that can lead to ketosis. Ketosis is a metabolic condition that affects production and health, and can occur clinically or subclinically. The aim of this thesis was to investigate the association of ketosis and the cow’s breed and parity to milk production and composition. Also the association of predicted NEFA, dry period, rest period and days open with ketosis, breed and parity was investigated. The data was acquired from ProAgria’s Maidosta Maitoon (MaMa) project, where 12 dairy farms had during two test periods tested milk’s BHB (β-hydroxybutyrate) concentration during the first seven weeks after calving. On each period, 20 animals per farm were participating and each animal’s production information came from Mtech Digital Solutions. NEFA values were predicted by using the milk fatty acid composition determined with mid-infrared (MIR) spectrometry. The animals were divided into four different groups based on the milk BHB concentration (≤ 50, ≤ 100, ≤ 200 and ≥ 500 µmol/L). The most common breeds on the farms, Ayrshire and Holstein, were included in the analysis. Parity was investigated by first comparing heifers with cows and then by dividing the animals into four different parity groups (1., 2., 3. and ≥ 4.). The milk production and composition were analyzed with repeated measures for the periods of 60 and 305 days in milk. The dry period, rest period and days open were analyzed with Friedman’s non-parametric variance analysis. The ketosis group did not affect daily milk yield during 60 or 305 days. Milk fat concentration was higher and protein concentration lower in groups with higher milk ketone concentration. Holstein cows had higher milk production than Ayrshire cows, and older cows had higher production than heifers. Milk production and ECM up to 60 days tended to increase by parity, peaking in the third parity group and decreasing in the fourth or higher lactation. Milk protein yield increased in Ayrshire cows in association with higher milk BHBA concentration, whereas the opposite was observed in Holstein cows (interaction breed x ketosis group, P = 0,045). The interaction between breed and parity tended to affect protein content, Ayrshire heifers had lower protein content than Holstein heifers but Ayrshire cows had higher protein content than Holstein cows. The predicted NEFA concentration increased by ketosis group. Holstein cows tended to have greater predicted NEFA concentrations than Ayrshire cows and heifers had significantly greater predicted NEFA concentrations than cows. Ketosis group affected the length of the dry period; the dry period was the longest in the third ketosis group. In addition, the length of the dry period was increased by parity. Ayrshire had shorter rest period and less days open than Holstein. Based on the results from this study, there was a difference between breeds on how ketosis affects milk production and milk composition. Further research is needed to understand the basis of the difference between breeds.