Factors influencing the reproductive capacity of a dairy herd

A note on a possible association between plasma β-carotene levels and conception rate in a group of winter-housed dairy cattle

Three groups of winter-housed Friesian cows were fed according to maintenance and production requirements on dairy cake and poor quality hay for 5 weeks (5 cows), 4 weeks (4 cows) or 2 weeks (3 cows). They were then treated as one group with two injections of 500 μg cloprostenol 11 days apart to synchronize oestrus, followed by insemination 72 and 96 h after the second treatment.

Blood samples were taken for β-carotene estimation 1 day before the first cloprostenol injection, 3 days before the second injection, and the day after the second insemination. Conception was confirmed by rectal examination. Haematological parameters and metabolic profiles for all 12 cows were in the normal range and condition scores showed no correlation with time of conception. However, plasma β-carotene levels declined rapidly and uniformly between the three sample points for all cows. The individual animal means were directly correlated with length of time on the described diet and with time of conception (P<005). A theory of β-carotene involvement in ovarian function is advanced.

Evaluation of two different oestrus-synchronisation methods with timed artificial insemination and resynchronisation of returns to oestrus in lactating Holstein cows

To examine the outcomes of adding medroxyprogesterone acetate (MAP) to the ovsynch protocol with the traditional ovsynch protocol in both cycling and anoestrus cows, and to evaluate a resynchronisation protocol, 742 cows averaging more than 40 days postpartum were assigned to the following four treatments: (1) ovsynch (OVS): day 0: GnRH; day 7: PGF2alpha; day 9: a similar dose of GnRH; day 10: timed artificial insemination (TAI), approximately 16-20h later; (2) ovsynch+MAP (MAP): the same ovsynch protocol plus an intravaginal insert made of polyurethane sponge impregnated with 300mg of MAP immediately after the first GnRH treatment and on day 7, at the time of the PG treatment, the sponge was removed; (3) resynchronisation (MAP+ODB): 1mg of oestradiol benzoate (ODB) on day 13 after TAI and a new sponge impregnated with MAP was inserted and; on day 20, 1mg of ODB was given and the sponge removed; and (4) no resynchronisation (No MAP): only oestrus detection and AI at any repeat oestrus detected after TAI. Progesterone was measured in milk samples collected on days -17, -10, -3, 13 and 20 (TAI=day 0). Based on milk P4 at days -17 and -10, 27.4% of the cows were still anoestrus. At PG injection, 67.7% of the cycling and 21.3% of the anoestrus cows had elevated P4. Farm, days postpartum and parity variations were detected in both cases. On day 20 after TAI 42.6% of cycling and 8.3% of the anoestrous cows had elevated P4. Pregnancy rates were similar in both pre-breeding treatments (20%), but interactions (P<0.001) were detected between treatment and cycling activity (for anoestrous cows: MAP=34.9%; OVS=11.1%. Average interval from TAI to subsequent AI was 37+/-3 days. Resynchronisation resulted in more (P<0.001) cows in oestrus between days 18 and 25 after TAI. Conception rate in the MAP+ODB treatment was lower (P<0.05) than the No MAP group (22.8% versus 47.4%). It was concluded that the addition of a progestin to the ovsynch protocol resulted in increased pregnancy rates of cows treated during anoestrus. The benefit of including MAP with the ovsynch protocol for cycling cows is equivocal.

Effect of disease on reproduction in the dairy cow: a meta-analysis

Effects on reproduction of dystocia, stillbirth, abortion, milk fever, retained placenta, metritis, cystic ovaries, anestrus, ketosis, displaced abomasum, locomotor disorders, and mastitis were reviewed. Papers were considered if they provided quantitative estimates of diseases on days to first estrus, days to first service, conception rate at first service, days from first service to conception, days to conception or days open, calving interval, conception rates at various days post partum (dpp), and number of services per conception or per cow. Only papers in English in peer-reviewed journals were selected for analysis of post 1960 data from intensive dairy regions. Seventy papers fulfilled the selection criteria. Summary estimates of disease effects were calculated according to meta-analysis methods, and study designs were described in detail to identify possible heterogeneity of the results. Stillbirth, milk fever, displaced abomasum and mastitis had no effect on reproduction. Clinical ketosis, dystocia and retained placenta were associated with 2 to 3 more days to first service and with a 4 to 10% lower conception rate at first service, resulting in 6 to 12 more days to conception. Locomotor disorders were associated with an average increase of 12 d to conception, with wide variation depending on lesions and stage of occurrence. Metritis was associated with 7 more days to first service, 20% lower conception rate at first service, resulting in 19 more days to conception. Cystic ovaries were associated with 6 to 11 more days to first service and with 20 to 30 more days to conception. Anestrus was associated with 26 more days to first service and with an 18% lower conception rate at first service, resulting in 41 more days to conception. Abortion was associated with 70 to 80 more days to conception.

A case-control study to identify farm factors affecting fertility of dairy herds: univariate description of factors

OBJECTIVE

To identify farm factors which were associated with reproductive performance in dairy herds in New South Wales.

PROCEDURE

A survey was administered by face to face interview to examine the responses of producers drawn from 757 herds, which used the New South Wales Agriculture Department Dairy Herd Improvement scheme. A case-control approach was used to select a total of 126 herds from the first (top group-cases) and fourth quartiles (low group-controls) for intercalving interval.

RESULTS

We found that the estimated interval from calving to first mating was significantly different between group (P = 0.03) and that the groups significantly differed in both their target for interval to first mating (P = 0.02) and their perceived optimum time for first mating (P = 0.04). Other factors associated with a longer intercalving interval included, use of embryo transfer programs (P = 0.08), younger managers (P = 0.02), fewer breedings per day (P = 0.01), a greater number of people detecting heats (P = 0.07), but less hours spent detecting heats while handling the cows (P = 0.11), and a failure to vaccinate bulls for campylobacteriosis (P = 0.14).

CONCLUSIONS

Managers of herds with poorer reproductive performance did not intend to mate cattle as soon after calving as managers with better reproductive performance, were not as active in seeking veterinary advice on reproduction, and were attempting to treat reproductive diseases and disorders themselves.

Reproductive performance of dairy herds infected with Leptospira interrogans serovar hardjo relative to the year of diagnosis

To assess the impact of Leptospira interrogans serovar hardjo infection on the reproductive performance of nine dairy herds with evidence of infection, forty years' fertility data were analysed relative to the year of first diagnosis. Fifty per cent of various fertility variables had their lowest values only in the year of diagnosis. Culling rates were highest during the year of diagnosis in five of the herds, and were above 22 per cent in five of nine (55-6 per cent) of the diagnosis years considered compared with seven (22-6 per cent) of the 31 non-diagnosis years. An assessment of the fertility status of the herds by means of a formula with incorporated the first service conception rate, the number of services per conception for cows conceiving, the calving to conception interval and the culling rate, revealed low reproductive performance during the year of diagnosis in six of the nine herds. Abortion rates were highest in four of the herds during the year of diagnosis, and these included the herds in which the fertility status was not lowest. It was concluded that L. interrogans serovar hardjo affected reproductive adversely by causing both abortions and low fertility, but that the effect was temporary.

Reproductive performance in South Australian dairy herds

Herd breeding records (161) were examined from a random 10% sample of dairy farms (96) in South Australia with more than 40 cows and suitable breeding records for 1988 and/or 1989. Of these farms, 53 (55.2%) had a year-round calving pattern, 42 (43.8%) claimed to be seasonal and one was changing from a year-round to a seasonal pattern. Only 14.6% of farmers observed oestrous behaviour outside milking times and 18.8% used tailpaint. Overall, the average proportion of unobserved heats was estimated to be 32%. Artificial insemination (AI) was carried out on 85.4% of farms (16.7% used AI alone and 68.7% also used bulls) of which 32.9% used commercial technicians and 67.1% were do-it-yourself operators. Overall, the average 30-day submission rate was 59.9% and the average 49-day non-return to service rate was 58.9%. Investigation into the probable causes of suboptimal reproductive performance gave a tentative diagnosis of inefficient oestrous detection, deferral of service, inadequate nutrition, poor AI technique, insufficient bulls, and venereal/other diseases in 69.1, 32.1, 27.2, 28.4, 13.6 and 7.4% of records, respectively.

Non-infectious factors affecting the presentation of dairy cows to artificial insemination and the result of mating in south western Victoria

The records kept by 4 artificial breeding centres in south western Victoria were examined and analysed by multiple regression analysis to determine whether daily fluctuations in the number of dairy cows presented for insemination, and daily, monthly and annual fluctuations in the result of first service, were associated with either climatic conditions or nutritional factors assessed as the availability of conserved hay and oats as feed supplements in the district. Over a 122 day observation period from July to October 1974, the number of cows presented daily for insemination was negatively correlated with daily rainfall total (p less than 0.01), wind speed (p less than 0.001) and barometric pressure (p less than 0.05). When the mean value for barometric pressure was used in the regression equation, rainfall totals and wind speeds above zero were associated with a mean reduction of 13.8% in the number of cows presented daily for insemination. The daily percentages of cows not resubmitted for service within 60 days of first service (non-return rates) were unrelated to climatic conditions and to the number of cows presented for insemination. The monthly non-return rate had a negative correlation (p less than 0.001) with the cost of oats but was not related to corresponding climatic changes. Annual non-return rate fluctuations were negatively correlated with the cost of oats (p less than 0.001) and with the July to October rainfall total (p less than 0.01). It is suggested that the correlation of non-return rate with the July to October total rainfall was due to an effect of rainfall total on the nutritional value of the pasture.

The use of progesterone administered intravaginally and pregnant mare serum gonadotrophin given by injection in controlled breeding programs in beef and dairy cattle

Five experiments involving 1,244 cows and heifers were carried out to investigate the factors which might influence the calving performance to fixed-time artificial insemination following intravaginal administration of progesterone (PRID) and intramuscular injection of pregnant mare serum gonadotrophin (PMSG). Factors examined were duration of PRID treatment, time of treatment after calving, time and dose PMSG and lactational status. Experiments 1, 2 and 3 were carried out on milked Friesian cows, experiment 4 on Friesian heifers and experiment 5 on suckled and dry Herefords. All cows were inseminated once with frozen/thawed semen 54 to 58 h or 46 to 50 h after completion of PRID treatment. Overall there was a progressive increase in calving rates with an increase in the duration of treatment from 12 to 14 to 16 days but there was little or no effect of time after calving (4 v 7 weeks) at which treatment was commenced. The poorer calving performance of cows treated for 12 to 14 days was associated with relatively high peripheral levels of plasma progesterone at the time of the PRID removal, suggesting the presence at the end of treatment of residual secretory luteal tissue. There was an effect on calving performance of PMSG given at the time of PRID removal but its effect varied according to the duration of PRID treatment. After 12 days treatments (experiments 1 and 5) PMSG had little effect, whereas after 14 days treatments, 0, 500 and 750 IU PMSG gave calving rates of 27%, 40% and 46% in experiment 2 and 5%, 24% and 38% in experiment 5.(ABSTRACT TRUNCATED AT 250 WORDS)