Advances in bovine theriogenology in New Zealand. 2. Breeding management and technologies for improved reproduction

Expanding the dairy herd in pasture-based systems: The role of sexed semen within alternative breeding strategies

A simulation model was developed to determine the effects of sexed semen use in heifers and lactating cows on replacement heifer numbers and rate of herd expansion in a seasonal dairy production system. Five separate artificial insemination (AI) protocols were established according to the type of semen used: (1) conventional frozen-thawed semen (CONV); (2) sexed semen in heifers and conventional semen used in cows (SS-HEIFER); (3) sexed semen in heifers and a targeted group of cows (body condition score ≥3 and calved ≥63 d), with conventional semen used in the remainder of cows (SS-CONV); (4) sexed semen in heifers and a targeted group of cows, with conventional semen in the remainder of cows for the first AI and conventional beef semen used for the second AI (SS-BEEF); or (5) sexed semen in heifers and a targeted group of cows, with conventional semen in the remainder of cows for the first AI and short gestation length semen used for the second AI (SS-SGL). Each AI protocol was assessed under 3 scenarios of sexed semen conception rate (SS-CR): 100, 94, and 87% relative to that of conventional semen. Artificial insemination was used on heifers for the first 3 wk and on cows for the first 6 wk of the 12-wk breeding season. The initial herd size was 100 cows, and all available replacement heifers were retained to facilitate herd expansion, up to a maximum herd size of 300 cows. Once maximum herd size was reached, all excess heifer calves were sold at 1 mo old. All capital expenditure associated with expansion was financed with a 15-yr loan. Each AI protocol was evaluated in terms of annual farm profit, annual cash flow, and total discounted net profit. The SS-CONV protocol generated more replacement heifers than all other AI protocols, facilitating faster expansion, and reached maximum herd size in yr 9, 9, and 10 for 100, 94, and 87% SS-CR, respectively. All AI protocols, except SS-BEEF and SS-SGL at 87% SS-CR, reached maximum herd size within the 15-yr period. Negative profit margins were experienced for SS-CONV in the first 5, 4, and 3 yr of expansion for 100, 94, and 87% SS-CR, respectively. Total discounted net profit was greater in all sexed semen AI protocols compared with CONV. This study demonstrated that, for each SS-CR, the greatest rate of expansion is achieved when using sexed and conventional semen (SS-CONV). The combined use of sexed semen and beef (SS-BEEF) or SGL (SS-SGL) semen resulted in greater discounted net profit at 100, 94, and 87% SS-CR compared with CONV, but a similar net worth change at 87% SS-CR due to a lower inventory change because SS-BEEF and SS-SGL reached maximum herd size within 15 yr.

Reproductive performance of seasonal-calving, pasture-based dairy herds in four regions of New Zealand

AIMS

The primary objective of this study was to describe the reproductive performance of a selection of New Zealand dairy herds in 2009/10 and 2010/11. A secondary objective was to explore associations between a number of biophysical and socio-demographic herd-level variables and herd-level reproductive outcomes.

METHODS

Seasonal-calving, pasture-based herds from the Waikato (n=16), Taranaki (n=16), North Canterbury (n=17) and South Canterbury (n=14) regions of New Zealand were enrolled as part of a larger study. Submission, conception and pregnancy risks ("in-calf risks") were calculated for 2009/10 and 2010/11 based on cow-level records and from the results of strategically timed pregnancy diagnoses. Additional herd-level information was collected during interviews with the herd key decision maker (KDM). Associations between independent variables and reproductive performance were examined using univariable and multivariable generalised linear models.

RESULTS

Mean 6-week in-calf risk of the herds over both study years was 67 (min 46, max 86)%, mean 3-week submission risk was 81 (min 44, max 95)% and mean probability of pregnancy at first insemination was 48 (min 25, max 71)%. On univariable analyses, the herd's 6-week in-calf risk in the year before enrollment (2008/09) was the strongest identified predictor of each of submission risk, probability of pregnancy at first insemination and 6-week in-calf risk (all p<0.01), while other predictor variables considered were non-significant. From multivariable modelling, herds using extensive production systems had better reproductive performance than more intensively managed systems. Higher 3-week submission risks were achieved in herds where the KDM were farm managers rather than owner operators, and where the predominant breed was Jersey rather than Friesian.

CONCLUSIONS

The New Zealand dairy industry has set a target for a mean 6-week in-calf risk of 78%, with minimal hormonal intervention, by 2016. Achieving this target appears unlikely unless there are substantial increases in both submission risks and pregnancy at first inseminations. The mean 6-week in-calf risk of New Zealand dairy herd does not appear to have changed in the last decade. However the large differences between herds indicate that better reproductive performance is currently possible in many herds. The herd's 6-week in-calf risk in the year before enrollment (2008/09) was the strongest identified predictor of current 6-week in-calf risk, suggesting that rate of improvement in reproductive performance would be slow within current management systems unless substantial changes are introduced.

A longitudinal study of reproductive performance and management of 82 dairy herds in the Waikato region with differing policies on the routine use of induction of parturition

AIMS

To describe the reproductive performance and management practices over three lactations in dairy herds that had different policies on the routine use of induction of parturition; to describe any change in outcomes in herds that ceased inductions during the study period; and to investigate other herd-level factors associated with reproductive performance.

METHODS

From 2002 to 2004 inclusive, a longitudinal study was undertaken in 82 herds in the Waikato region of New Zealand. The main outcome variables were the percentage of cows pregnant after 8 weeks of mating (8-week in-calf rate) and the percentage of cows not pregnant at the end of mating (final empty rate). Data were obtained from pregnancy diagnosis records from a veterinary practice and from an electronic database, and a questionnaire. Herds were classified as either not using inductions in the three lactations (Nil; n=14), ceased inductions in the second or third lactation (Transitional; n=12), or continuing to induce (Continuing; n=56).

RESULTS

Nil herds had a higher 8-week in-calf rate (p=0.01) than Transitional or Continuing herds (83%, 78% and 79%, respectively). The final empty rate in Nil and Transitional herds was similar (10.2% and 9.9%), tended to be greater in Nil than in Continuing herds (10.2% vs 9.0%; p=0.06) and was greater in Transitional than in Continuing herds (9.9% vs 9.0%; p=0.04), respectively. Multivariable modelling found that 8-week in-calf rates were additionally associated with year of lactation, interval from the planned start of calving (PSC) to the median calving date, duration of artificial insemination, and 21-day submission rate; and that final empty rates were associated with year of lactation, predominant breed, percentage of the herd calving within 40 days of the planned start of mating (PSM), the total duration of mating, and the 21-day submission rate, but not the herd induction policy. A change to ceasing routine use of induction tended to be associated (p=0.07) with a 2.5% increase in the final empty rate in the lactation of change.

CONCLUSIONS

The reproductive performance of herds was associated with induction policy, in addition to other factors. Herds that ceased induction had a greater 8-week in-calf rate but a greater final empty rate than those that continued. The higher empty rate in Nil herds was partly due to their shorter duration of mating.

CLINICAL RELEVANCE

Herdowners and their advisors planning to cease routine use of induction should plan for an increase in the final empty rate in both the lactation of change and in the longer term, and undertake measures to mitigate against this effect.

Use of equine chorionic gonadotrophin in synchronised AI of seasonal-breeding, pasture-based, anoestrous dairy cattle

In seasonally calving dairy areas, a critical index of efficiency and profitability is the ability to maintain a short annual calving spread. In essence, this means that all cows need to conceive within 90 days of calving. Anovulatory anoestrus (AA) is a major barrier to reproductive performance under these conditions and the successful treatment of AA is an important aspect of reproductive intervention. The present paper reviews regimens used to treat AA in New Zealand and reports on a large-scale field trial investigating the effects of equine chorionic gonadotrophin (eCG) within a proven efficacious treatment protocol. The administration of eCG at the time of removal of a progesterone-releasing device in an 8-day, oestradiol benzoate (EB)-based treatment protocol increased the percentage of cows in calf after 7 and 28 days of breeding. The interaction between cow age and treatment with eCG was significant, with cows over 5 years of age having higher conception rates (P = 0.002) and 7 day in-calf rates (P = 0.002) than cows on a standard 8-day treatment protocol without eCG. The addition of eCG to a standard 8-day EB/progesterone protocol can improve reproductive success in seasonally calving AA dairy cows.