Comparison of diagnostic approaches, and a cost-benefi t analysis of different diagnostic approaches and treatments of anoestrous dairy cows

Abstract

AIM: To compare diagnostic techniques, and to assess the economic effects of diagnosing and treating dairy cows not detected in oestrus before the planned start of mating (PSM).

METHODS: Cows from 12 herds were defined as anoestrus at Day -9 (where Day 0=PSM) based on presence of tail paint that had been applied at Day -35. The presence of a corpus luteum (CL) was diagnosed by palpation or ultrasonography on Day -9, or by determining the concentration of progesterone (P4) in milk at Days -16 and -9. Cows with concentrations of P4 in milk >1 ng/ml at one or both times were defined as CL+. Cows were randomly assigned to be treated with (a) nothing (Control; n=558); (b) gonadotrophin-releasing hormone (GnRH) on Day -9, prostaglandin F2_α (PGF2_α) on Day -2, and GnRH on Day 0, with set-time artificial insemination (AI) 16-20 h after the second GnRH treatment (Ovsynch; n=553); or (c) as for (b) but with placement of an intravaginal P4-releasing device on Day -9, and removal on Day -2 (Ovsynch+P4; n=551). Cows detected in oestrus between Day -2 and the second GnRH treatment did not receive the second GnRH treatment. Pregnancy diagnosis took place on three occasions, and the date of conception estimated, from which the PSM-to-conception interval was calculated. Agreement between the three diagnostic techniques for CL status was evaluated using Kappa analyses, and sensitivities and specificities were calculated using a Bayesian Monte Carlo approach that does not assume a gold standard. Partial budgets and decision trees were constructed to assess the costeffectiveness of diagnosis and treatment.

RESULTS: The level of agreement was higher between ultrasonography and concentration of P4 in milk (0.64) than for palpation and ultrasonography or concentration of P4 in milk (0.50 and 0.49, respectively). The Ovsynch+P4 treatment had a higher nett benefit than Ovsynch relative to no treatment (NZ$80.40 and NZ$47.50/cow treated, respectively) in the absence of diagnosis of CL status. Following diagnosis, the Ovsynch+P4 treatment remained the most cost-effective option for both CL+ and CL- cows. It was concluded that the Ovsynch+P4 treatment without any diagnostic procedure was the most cost-effective option.

CLINICAL RELEVANCE: Treatment of anoestrous cows was more cost-effective than no treatment, with Ovsynch+P4 more cost-effective than Ovsynch in cows with or without a CL. Differentiation of anoestrous cows into CL+ and CL- groups for treatment was not cost-effective.

KEY WORDS:

• Dairy cattle
• anoestrus
• treatment
• economics

Acknowledgements

The cooperation of the herdowners involved in this study is much appreciated. The technical support of Laura Clausen, Katie Carnie, Sarah Clune, Murray Edgar, Alfred Gerrits, Vickii van Gog, Ondine Habgood, Jirigala Menghe, Rhonda Plant, Cathy Yanez, and Angela Sheehan is also appreciated. Veterinary procedures (ovarian palpation, ovarian ultrasonography and pregnancy diagnosis) were undertaken by Chris Compton, Andrew Gore, John McCarthy, Angela McEwan, Geoff Plant, Katrina Roberts and Matt Wells, all of the Animal Health Centre.

The study was funded by DairyNZ, DairyAustralia, Bomac Laboratories, and Pfizer Animal Health. Half of the progesterone devices, GnRH and PGF_2α were supplied by Bomac Laboratories Ltd, and the other half of the progesterone devices by Pfizer Animal Health.