Investigations of factors that influence oestrus expression in dairy cattle
Zebari, H.M. (2019) Investigations of factors that influence oestrus expression in dairy cattle. Doctoral thesis, Harper Adams University.
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Abstract
Oestrus expression and detection are keyin the reproductive management ofdairy 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 from15 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 cowtime 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 wereincreased(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 durationof 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 1stoestruspostpartum (PP)with a lower intensity of oestrus expression on the day of oestrus compared to 2ndand ≥3rdoestrus PP. More steps and a lower lying (P<0.001) time with a longer oestrus duration (P=0.004) were recordedwhen three cows ormore were in oestrus (SG3+) simultaneously comparedto onecow (SG1) in oestrus. Also a highernumberof steps (P<0.001) were takenwhen two cows (SG2) were in oestrus comparedto SG1. More steps(P<0.001) were recordedin 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 stepstaken wasincreasedwhile 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 withalonger oestrus duration insummer 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 concentrationsincreased 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). AbstractiiThe fourth study was designed to determine the milk fatty acid profileof dairy cows during oestrus and day 14 of the dioestrus period and their relationship with oestrus activity. Milk samples were analysedfor fatty acid concentrationsusing gas GC. On the day of oestrus, the concentrationof acetic acid (P<0.001), valeric acid (P=0.016), caproic acid (P<0.001) and myristoleic (P=0.035) werehigher in milk compared to day14after 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 showedbehavioural oestrus. Time budgets of the cowsshowing behavioural oestrus were disrupted with a lowerlying 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 numberof oestrus post-partum,SG, BCS, LS, parity, season and E2 concentrations. Concentrations of some milk FAwere also affected.Further research is needed to determinewhether these could become part of our oestrus detection arsenal.
| Item Type: | Thesis (Doctoral) |
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| Divisions: | Animal Production, Welfare and Veterinary Sciences (to 31.07.20) |
| Depositing User: | Ms Kath Osborn |
| Date Deposited: | 10 Dec 2019 14:20 |
| Last Modified: | 10 Jan 2020 05:10 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/17480 |
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