Vulnerability in Holstein-Friesian dairy cows : risk factors for culling and effect of temperament on oestrus
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The general aims of the work were to determine the factors associated with vulnerability in Holstein- Friesian dairy cows in two scenarios: A) culling and B) the effect of temperament on days to first recorded oestrus in dairy cows. Vulnerability was defined as either an increased risk of being culled or having long interval from calving to first recorded oestrus in cows. The work was carried out in two distinct studies. The objective of the first study was to identify the predisposing factors for an increased risk of culling in adult Holstein-Friesian dairy cows. This study was conducted using data sourced from Scottish Agricultural College Langhill database. Between September 2003 and August 2010, 519 cows calved for the first time and 175 of these were culled. The major reasons for culling were fertility (9.2%), udder problems (9.1%) and accident (6.2%) on which further analysis was performed. The culled cows were matched with their cohorts that survived to a later lactation. Cows assessed for the risk of being culled due to major reasons had a mean age at first calving of 26.2 months (Standard Deviation (SD) =2.4). Cows with high body condition score (BCS) at service and low 60-day (60d) milk protein had a significantly (P<0.05) increased likelihood of being culled due to infertility. The regression estimate (RE) was 1.67 for Service BCS and -2.43 for 60d milk protein with predicted probability (PP) of 0.91. However in first lactation heifers, only BCS at service was significant (P<0.05, RE=2.65 and PP=0.86). Cows with a reduced interval to reach peak milk yield had a significant (P<0.01) likelihood of being culled due to udder problems (RE=-0.05 and PP= 0.89). Locomotion score and parity were not significant on increasing the risk of culling cows due to accident. Hence higher BCS at service, low 60d milk protein and short duration to peak lactation are factors that place dairy cows at an increased risk of being culled. The second study aimed at determining the association between temperament and days to first recorded oestrus in adult dairy cows. Temperament traits that were studied were flight response score, nervous, interest, shy, bold, fear and docile. Number of days to first recorded oestrus after calving was the dependent variable in the analysis. Seventy Holstein-Friesian dairy cows, mean age at first calving 25 months (SD=1.9) were used in the study. Temperament traits for individual cows were recorded on day 30 before calving, and on days 30 and 60 after calving. Temperament traits were quantified using an Approach Passageway test. On average the first oestrus occurred 55.5 days (SD=17.9) after calving. The study showed that temperament traits did not significantly affect the number of days to first recorded oestrus. Within the temperament traits, nervousness, shyness, boldness, fearfulness and docility were significantly (P<0.001) related to flight response score while interest was not. In conclusion, higher than average BCS at service, low milk protein content at day 60 in lactation and short duration to peak lactation exposes cows to an increased risk of being culled while temperament did not influence number of days to first recorded oestrus after calving.