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Title: Investigations of factors that influence oestrus expression in dairy cattle
Author: Zebari, Hawar Mikahil Hassan
ISNI:       0000 0004 8503 5164
Awarding Body: Harper Adams University
Current Institution: Harper Adams University
Date of Award: 2019
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Oestrus expression and detection are key in the reproductive management of dairy cows where AI is routinely used. Over the past 50 years, the percentage of dairy cows in oestrus that stand to be mounted has declined from 80% to 50% and the duration of oestrus has fallen from 15 h to 5 h. Furthermore, many cows show only the secondary signs of oestrus or do not show behavioural signs (silent oestrus). The first study was designed to determine whether cow time budgets were affected by behavioural and silent oestrus in lactating dairy cows. Of the 40 behavioural oestrus events that were detected, the number of steps were increased (P < 0.001) compared to three days before and three days after oestrus, whilst the percentage of lying time, the number of lying bouts, DMI, feeding duration and the number of visits to feed were reduced (P < 0.001). On the day of silent predicted oestrus, only the duration of feeding was reduced (P < 0.03). The second study was designed to investigate factors affecting the strength of oestrus expression in dairy cows. The duration of oestrus was shorter (P=0.051) in 1st oestrus postpartum (PP) with a lower intensity of oestrus expression on the day of oestrus compared to 2nd and ≥3rd oestrus PP. More steps and a lower lying (P < 0.001) time with a longer oestrus duration (P=0.004) were recorded when three cows or more were in oestrus (SG3+) simultaneously compared to one cow (SG1) in oestrus. Also a higher number of steps (P < 0.001) were taken when two cows (SG2) were in oestrus comparedto SG1. More steps (P < 0.001) were recorded in body condition score (BCS) 2.75 cows compare to BCS ≤2.5 and BCS ≥3. On the day of oestrus, more steps but a lower lying time and fewer lying bouts (P < 0.001) were recorded with a longer oestrus for cows of parity ≤2. The number of steps taken was increased while lying time, and lying bouts decreased (P < 0.001) with increase locomotion score (LS). Oestrus duration was longer with a higher (P < 0.001) intensity in cows that had locomotion score one (LS1). This study also found cows spent more time (P < 0.001) walking with a longer oestrus duration in summer compared to other seasons. To further investigate the factors that affect oestrus, the third study was designed to determine the relationship between milk oestradiol (E2) concentration and oestrus activity. Of the 39 oestruses detected from milk progesterone (P4) concentrations, 28 oestruses were behavioural and 11 were silent. Of the 28 behavioural oestruses, milk E2 concentrations increased from 2.0±0.5 pg/mL to 8.2±1.1 pg/mL on the day of oestrus. Milk E2 concentrations were significantly lower 1.3±0.2 pg/mL during silent oestrus compared to behavioural oestrus. Overall there was a positive relationship between milk E2 concentrations and the number of steps taken (r2=0.73; P < 0.001). The fourth study was designed to determine the milk fatty acid profile of dairy cows during oestrus and day 14 of the dioestrus period and their relationship with oestrus activity. Milk samples were analysed for fatty acid concentrations using gas GC. On the day of oestrus, the concentration of acetic acid (P < 0.001), valeric acid (P=0.016), caproic acid (P < 0.001) and myristoleic (P=0.035) were higher in milk compared to day 14 after oestrus. However, on day 14 after oestrus, arachidonic acid concentrations in milk were higher (P=0.004) compared to the day of oestrus. In conclusion, from all these studies, approximately 59.9% of cows showed behavioural oestrus. Time budgets of the cows showing behavioural oestrus were disrupted with a lower lying time, feeding time but a higher number of steps per day. In cows undergoing silent oestrus, just feeding time was affected. Factors that affect oestrus intensity include the number of oestrus post-partum, SG, BCS, LS, parity, season and E2 concentrations. Concentrations of some milk FA were also affected. Further research is needed to determine whether these could become part of our oestrus detection arsenal.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available