MILK DEVELOPMENT COUNCIL REPRODUCTIVE PERFORMANCE OF THE HIGH GENETIC COW

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1 MILK DEVELOPMENT COUNCIL REPRODUCTIVE PERFORMANCE OF THE HIGH GENETIC COW Project No. 97/R5/05

2 FINAL REPORT TO MDC 97/R5/O5 FEEDING AND SELECTION OF HIGH GENETIC MERIT (HGM) COWS TO MAXIMISE FERTILITY Start date: 1 October 1997 End date: 31 December 2000 PROJECT LEADER: Professor DC Wathes, Department of Veterinary Basic Science, Royal Veterinary College, Boltons Park, Hawkshead Road, Potters Bar, Herts EN6 1NB IN COLLABORATION WITH: Professor DE Beever, Department of Agriculture, University of Reading, Earley Gate, PO Box 236, Reading, RG6 6AT (Centre for Dairy Research, CEDAR) Main participants: RVC: Ms VJ Taylor CEDAR: Mr AJ Hattan Other contributing staff: RVC: Mr PGA Pushpakumara, Mrs A Zhang CEDAR & APRU: Dr MJ Bryant, Dr NH Gardner, Ms SL Gore, Mr AK Jones, Mr DT Juniper, Dr CK Reynolds, Ms CH Whittaker

3 Section 1. EXECUTIVE SUMMARY The aims of the project were: To investigate the extent to which fertility is compromised in high genetic merit cows by detailed monitoring of ovarian function; To examine the relationship between energy balance, metabolic hormone levels and reproductive performance in individual cows; To assess the possibility of using measurement of metabolic hormones in heifers to predict future yield and reproductive performance. During the course of the project, four inter-related studies were performed. All investigated the relationships between milk production, metabolic measurements and fertility from 1-3 weeks pre-calving until weeks post calving in lactating dairy cows. Fertility monitoring was based on milk progesterone profile analysis. Detailed information was obtained from a total of 182 lactations. Study 1 Relationships between transition diet, metabolic parameters and fertility in cows of average genetic merit (AGM); Study 2 A comparison of metabolic characteristics and ovarian function in cows of average and high (HGM) genetic merit; Study 3 The effect of different diets on metabolic characteristics and ovarian function in HGM cows; Study 4 Assessment of metabolic parameters in pre-pubertal heifers and their relationships to subsequent milk production and fertility. The major findings are summarized as follows. 1. The effect of genetic merit (data derived from all 4 studies) 1.1. The incidence of abnormal progesterone profiles doubled from 32% in AGM cows to 64% in HGM cows. Within the abnormal profile category there was an even split between cows with long periods of low progesterone (Low P 4 ) defined as delayed ovulation before (DOV1) or after (DOV2) the first ovulation post partum and cows with prolonged periods of luteal activity >19 days in the first (PCL1) or subsequent (PCL2) cycles. The incidences were: AGM, Low P 4 13%, PCL 18%; HGM, Low P 4 31%, PCL 33% and first lactation heifers, Low P 4 29%, PCL 26%. Combining data from studies 1-3, fertility data were consistently worse in HGM than AGM cows. (Table 1.1). The cost to the dairy farmer of the prolonged service to conception interval and greater number of services per conception 1

4 required by HGM in comparison with AGM cows can be estimated at about 3000 per 100 cows, based on calculations published by Esslemont and Kossaibati (1999). This does not include extra veterinary costs likely to be incurred because of the higher incidence of irregular cycles. Table 1.1 Summary of fertility data of all cows in the studies. First lactation heifers (n=38) AGM cows (n=60) HGM cows (n=84) Difference HGM vs AGM Interval to 1 st P 4 rise (days) 30 ± ± 1.2 b 33 ± 3.4 a +12 days Abnormal P 4 profiles (%) 55% 32% b 64% a +32% 1 st service conception rate 34% 40% 37% -3% Services per conception 2.1 ± ± ± Days open 135 ± ± 6.6 d 117 ± 5.7 c +12 days Comparison of AGM & HGM: a>b, P<0.01; c>d, P< HGM cows lost more weight after calving than AGM cows and had a longer and deeper period of negative energy balance (NEB). This was associated with lower concentrations of circulating insulin-like growth factor-i (IGF-I) and insulin, particularly in the first few weeks post partum Within the HGM cows higher yield was associated with an increased incidence of abnormal progesterone profiles. This relationship was not present in AGM cows or heifers. However, heifers with abnormal progesterone profiles had higher milk fat and lower milk protein concentrations Combining data from all the AGM and HGM cows studied, the incidence of abnormal progesterone profiles was 32% (29/90) in cows producing peak yields of <50 kg/day compared with 67% (36/54) in those producing > 50 kg/day (χ 2 test, P<0.01) There was a significant negative relationship between yield and IGF-I levels after calving Therefore, although some high yielding cows were able to maintain adequate fertility, in the majority of cows achieving peak yields of > 50 kg/day milk, fertility was compromised. 2

5 2. Relationships between production and metabolic parameters and fertility (data derived from all 4 studies) 2.1. Both DOV1 and DOV2 progesterone profiles are indicative of a failure to ovulate at the appropriate time. The underlying physiology generally appeared quite similar, so both are considered together. This condition was consistently associated with: Low dry matter intakes (DMI); Low body condition scores, either because cows calved in poor condition or lost a significant amount of condition shortly after calving; Low IGF-I, particularly in the pre-service period (weeks 1-7 post partum); 2.2. There were also strong indications of underlying metabolic disturbances in the PCL cows. Study 1 lower IGF-I than in normal profile AGM cows; Study 3 high milk lactose and blood insulin, and reduced body weights in HGM cows; Study 4 low IGF-I in heifers; this was frequently associated with a uterine infection Cows which failed to conceive despite several AI attempts were characterised by a large drop in BCS after calving, a higher milk fat % and lower IGF-I concentrations for 15 weeks after calving Therefore, cows with a low DMI, low BCS and/or a uterine infection generally had reduced IGF-I levels. This appears to impair fertility, either by preventing ovulation (Low P 4 ), by delaying luteolysis (PCL) and/or by reducing conception rates. The latter could be associated with deleterious effects on the developing oocyte and/or the early embryo. 3. The effect of diet (data derived from studies 1 and 3) 3.1. The different transition and lactation diets investigated affected milk production parameters. This was considered in a related MDC funded project (97/R2/05) and is not presented further here The diets did not, however, have a major impact on fertility, as differences between the responses of individual cows on the same diet were more marked than differences between diets. It should, however, be noted that all the diets used had been balanced to meet protein and energy requirements and we would anticipate that failure to meet these requirements, probably due to impaired feed intake, would 3

6 have a deleterious effect on fertility. In such situations, it is likely that body tissue loss to support lactation demand will increase. 4. Predictive value of metabolic monitoring in pre-pubertal heifers (study 4) 4.1. The GH response to a challenge of GH-releasing factor (GRF) was able to predict yield in low but not high pedigree index (PI) heifers. Whereas there was a positive correlation between GH and yield in low PI heifers, the trend was reversed in high PI heifers. The reason for this difference is unclear, but it suggests that factors other than predicted genetic merit limit yield in the first lactation in high PI animals Heifers which had high levels of glucose and low IGF-I when monitored prepubertally were more likely to experience low progesterone levels in their first lactation. It is possible that this indicates a degree of insulin resistance in these animals These results raise the possibility that monitoring of pre-pubertal heifers could be used to select for low PI animals with high potential for milk production and to select against heifers likely to experience fertility problems. 4

7 Section 2. Farmer recommendations 1. The relationship between higher peak yields (>50 kg/day) and reduced fertility is unambiguous. It is reflected in increasing services/conception as HGM cows experience more irregular cycles and lower conception rates. Although we did not specifically test this, we predict that delaying first service in HGM cows to approximately 100 days post partum would be more cost effective than earlier hormonal treatments which would be given at a time of compromised nutrient metabolism. By 100 days the cows are returning to positive energy balance, body condition is increasing and IGF-I levels have risen. The cost benefit of extra milk production per cow needs to be carefully balanced against the expense of the reduced fertility. 2. Some lower yielding cows may also experience fertility problems associated with low BCS, reduced DMI and low plasma IGF-I concentrations. However, the incidence is significantly less than in higher yielding cows. The recommendation would again be to delay first service in such animals. 3. Cows should be fed to calve at a BCS of , to exhibit controlled BCS loss and high DMIs during the first 100 days post calving. While BCS at calving can be manipulated fairly readily it is more difficult to control post-calving as the genetically determined production characteristics of individual cows appear to have a much greater influence than diet alone. Section 3. Industry recommendations It is clear from our work and that of others that the increase in milk production gained in Holstein cows has been accompanied by changes in the GH-insulin- IGF-I axis. This leads to a greater mobilisation of body reserves for milk production and a greater loss of body weight in early lactation. In the longer term it should be possible to discover genetic markers which will be of predictive value for both milk production and fertility parameters. This requires a greater knowledge of the underlying physiology to determine target genes. In the shorter term we recommend delaying first service in higher yielding cows and/or those of a low BCS (<2) post partum. As there is clearly a conflict between yield and fertility, the real economic benefits of high yields need to be calculated to take this into account. These calculations should establish a maximum yield above which there are no cost benefits. This information should be incorporated into sire selection. Our data strongly suggest that, while good nutrition is essential, it will not be possible to overcome all adverse effects of high yield on fertility by nutritional management alone as the underlying cause is primarily genetic. 5