New Zealand Veterinary Journal

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Conception rates to fixed-time artificial insemination of two oestrus synchronisation programmes in dairy heifers SK Sahu, TJ Parkinson & RA Laven To cite this article: SK Sahu, TJ Parkinson & RA Laven (2015) Conception rates to fixed-time artificial insemination of two oestrus synchronisation programmes in dairy heifers, New Zealand Veterinary Journal, 63:3, 158-161, DOI: 10.1080/00480169.2014.982740 To link to this article: http://dx.doi.org/10.1080/00480169.2014.982740

Accepted author version posted online: 30 Oct 2014. Published online: 13 Mar 2015. Submit your article to this journal

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Date: 05 November 2015, At: 13:52

New Zealand Veterinary Journal 63(3), 158–161, 2015

Scientific Article

Conception rates to fixed-time artificial insemination of two oestrus synchronisation programmes in dairy heifers SK Sahu*§, TJ Parkinson* and RA Laven*

Abstract

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AIM: To evaluate the conception rate to fixed-time artificial insemination (FTAI) of two oestrus synchronisation programmes in dairy heifers on eight farms over 2 years. METHODS: The study was conducted in 2008 and 2010 on eight farms near Palmerston North, New Zealand. Nulliparous Friesian and Friesian×Jersey heifers (13–15 months of age) were randomly allocated to one of two oestrus synchronisation programmes. Group 1 (GPG+P4; n=330), received gonadotrophin-releasing hormone (GnRH) I/M on Day 0, a progesterone (P4)-releasing intravaginal device from Days 0–7, prostaglandin F2α (PGF) I/M on Day 7 and a second dose of GnRH at the time of FTAI on Day 9. The second group (P4+PGF; n=343) received a P4-releasing intravaginal device from Days 0–7, PGF on Day 6 and FTAI on Day 9. Pregnancy was diagnosed from Days 42–52 by transrectal ultrasonography. RESULTS: The overall conception rate was 52.4% and 54.8% for the GPG+P4 and P4+PGF groups, respectively. The odds of conception for the two treatments were not different (OR=0.90; 95% CI=0.67–1.23), nor was there any difference between groups in different years (p=0.58). Farm affected conception rate (p=0.002), but there was no interaction with treatment (p=0.92) . CONCLUSIONS: This study has shown that an alternative synchronisation programme can produce similar results in terms of conception rate to the GPG+P4 treatment, currently commonly used in heifers. More research is required to establish whether other modifications to the GPG+P4 programme can produce similar results at lower costs, and to identify and quantify farm factors which affect the economic benefit of heifer synchronisation. CLINICAL RELEVANCE: This study indicated that synchronising heifers with P4 and PGF resulted in conception rates equivalent to those resulting from a GPG+P4 treatment, but with reduced drug costs. However, because heifers in the GPG+P4 group received the second GnRH injection at the

* Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand § Author for correspondence. Email: [email protected] http://dx.doi.org/10.1080/00480169.2014.982740 © 2015 New Zealand Veterinary Association

time of AI, they needed only three yardings as opposed to the four required for the heifers treated with P4 and PGF. Thus, the choice of programme for an individual farm will depend on that farm’s circumstances, in particular the cost of yarding the heifers. KEY WORDS: Oestrus synchronisation, heifer, conception rate, GPG, progesterone

Introduction Maiden heifers are the largest parity group in most dairy herds in New Zealand; they have the greatest genetic potential and, before their first calving, have incurred substantial costs to their owners without any return (Parker et al. 2007). In pasture-based dairy production systems, active reproductive management of these heifers can be difficult, particularly as they are often grazed on separate properties away from the main farm (Xu and Burton 1999a). Therefore, unlike lactating cows, which can be relatively easily observed and which can be checked, at least daily, when brought in for milking, special efforts have to be made to detect oestrus in heifers. Difficulties associated with the detection of oestrus have limited the widespread use of artificial insemination (AI) in maiden heifers in New Zealand. However, using AI in yearling heifers allows farmers to rear increased numbers of replacement heifers with high breeding-value. In turn, this allows for either a more rapid increase in herd size without buying in additional stock, or, if herd size remains constant, farmers can get the same number of high breeding-value replacements from a short AI period in the milking herd and, as a bonus, increase the rate of genetic gain of the herd (Macmillan 1998). Synchronising oestrus in dairy heifers under New Zealand conditions facilitates use of AI (Xu and Burton 1999b). In such animals, synchronisation programmes which do not require oestrus observation have significant advantages. Potential synchronisation programmes include those based on prostaglandin F2α (PGF) alone and those based on two injections of

AI FTAI GnRH GPG P4 PGF

Artificial insemination Fixed-time artificial insemination Gonadotrophin-releasing hormone Two injections of GnRH with one injection of PGF 2 days before the final GnRH Progesterone Prostaglandin F2α

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gonadotrophin-releasing hormone (GnRH) 9 days apart with an injection of PGF 2 days before the final GnRH treatment, (GPG; McDougall et al. 2013). For the latter protocol, addition of progesterone (P4) tends to improve conception rates in heifers (Peeler et al. 2004; Ambrose et al. 2005; Cavalieri et al. 2007), perhaps by reducing the proportion of premature ovulations (Rivera et al. 2004). McDougall et al. (2013) tested three oestrus synchrony programmes in dairy heifers in New Zealand; they found that combining a GPG programme with a P4-releasing intravaginal device and fixed-time artificial insemination (FTAI) at the time of the second GnRH injection resulted in a higher first service conception rate and 21-day pregnancy rate than the same programme with AI 24 hours later, or a double PGF protocol. As oestrus synchronisation is primarily used as a management tool for economic reasons, its use has to be justified based on improvements in submission and pregnancy rates, and the time between calving and conception compared to AI after oestrus detection (Laven et al. 2006). Increasing costs, such as by adding P4 may improve outcomes, but can still result in reduced economic benefit. Thus it is important to robustly test all synchronisation programmes to ensure that they produce the optimal benefits. An alternative synchronisation programme, which was not tested by McDougall et al. (2013), is combined use of P4 and PGF without GnRH. PGF treatment at the end of a 7-day P4 treatment was first proposed for synchronising oestrus by Deletang (1975). A modified programme with PGF being given 24 hours before P4 device removal, resulted in excellent synchrony of oestrus and high fertility in dairy heifers; with conception rates of 66% to a single FTAI, two days after PGF injection (Smith et al. 1984). The aim of this study was to compare the conception rate to FTAI of nulliparous dairy heifers under New Zealand management conditions treated with either GPG and P4 or P4 and PGF programmes.

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(morning) along with insertion of a P4-releasing intravaginal device containing 1.56 g of P4 (Cue-Mate, Bomac Laboratories Ltd) from Days 0–7 of the treatment. At the time of device removal on Day 7 (morning), heifers were given 500 µg cloprostenol I/M (Ovuprost, Bomac Laboratories Ltd). A second dose of gonadorelin (100 µg I/M) was given on Day 9 at the time of FTAI. Group 2 (P4+PGF; n=343) received a P4-releasing intravaginal device, as above, from Days 0–7, and 500 µg cloprostenol, I/M on Day 6 (morning). Fixed-time AI was performed in both groups on the morning of Day 9. In 2008, all semen was from Angus sires, whilst in 2010, Jersey or Friesian semen was used, depending on the farm. After the completion of FTAI, all groups of heifers were combined. Bulls were introduced to the heifers 7 days after FTAI, and remained with them until after pregnancy diagnosis. Pregnancy diagnosis was undertaken on Day 42–52 using a realtime B-mode ultrasound scanner (DP-6600 Vet, Mindray, Szechuan, China), equipped with a 7.5 MHz linear transducer. Conception date was confirmed by measuring crown rump length to determine the age of the conceptus. Conception rate was defined as the percentage of heifers that were confirmed to be pregnant to FTAI. Statistical analyses

Conception rate, determined from pregnancy diagnosis on Day 42–52, was treated as a binomial trait, and modelled using generalised linear mixed-model following a logit transformation. As farms were not repeated between years, two models were created. The first included the effects of treatment group, year and their interaction, and for the second model year was replaced by farm. Analyses were carried out using SAS v9.3 (SAS Institute Inc., Cary, North Carolina, USA). Least squares means and SE for each year or farm and treatment were obtained and used for the multiple comparisons.

Materials and methods

Results

All animal use was approved by Massey University Animal Ethics Committee, Palmerston North, New Zealand.

The overall conception rate was 52.4% and 54.8% for the GPG +P4 and P4+PGF groups, respectively (Table 1). The odds of conception for the two treatments were not different (OR=0.90; 95% CI=0.67–1.23). Model 1 analysis showed that there was no effect of treatment (p=0.54), year (p=0.12) or treatment by year interaction (p=0.79) on conception rate. The second model found that farm affected conception rate (p=0.002); however, there was no effect of treatment (p=0.67) or interaction (p=0.92) on conception rate.

Animals

The study was conducted in two years on eight farms in the vicinity of Palmerston North, in the lower North Island of New Zealand. In 2008 and 2010, nulliparous Friesian and Friesian×Jersey heifers 13–15 months of age were selected. The numbers of heifers enrolled from different farms is summarised in Table 1. Power analysis The number of animals used in the study was based on detecting an increase of more than 10% in conception rate after GPG and P4 compared to P4 and PGF programmes. With α=0.05, using 330 animals in each group resulted in β=0.83. Synchronisation protocols

All heifers were randomly allocated to one of two treatment groups. Group 1 (GPG+P4; n=330) received 100 µg of gonadorelin I/M (Ovurelin, Bomac Laboratories Ltd, Auckland, NZ) on Day 0

Discussion This is the first New Zealand-based study comparing the efficacy in heifers of the recommended GPG plus P4 protocol for oestrus synchronisation with a synchronisation programme using just P4 and PGF that is commonly used outside Australasia. In the present study, synchronising heifers with the latter protocol resulted in a similar overall conception rate to the former (54.8 vs. 52.4%).

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Sahu et al.

Table 1. Number of dairy heifers inseminated on different farms in 2008 and 2010 and diagnosed pregnant 42–52 days after fixed-time artificial insemination, following treatment with either GPG+P4 or P4+PGF synchronisation programmes. GPG+P4 Year

Farm

2008

1

29

17 (59)

31

19 (61)

2

17

12 (71)

21

16 (76)

3

65

43 (66)

69

42 (61)

4

44

15 (34)

46

19 (41)

Total

155

87 (56)

167

96 (58)

5

30

15 (50)

20

8 (40)

6

52

24 (46)

55

31 (56)

7

23

12 (52)

23

12 (52)

8

70

35 (50)

78

41 (53)

Total

175

86 (49)

176

2010

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Total for 2008 and 2010

Inseminated

P4+PGF

330

Pregnant (%)

173 (52.4)

Inseminated

343

Pregnant (%)

92 (52) 188 (54.8)

GPG + P4 = Treatment with progesterone (P4) for 7 days, with injections of gonadotrophin-releasing hormone (GnRH) on Days 0 and 9, and injection with prostaglandin F2α (PGF) on Day 7. P4 + PGF = Treatment with P4 for 7 days and injection with PGF on Day 6.

The conception rates reported in this study for both synchronisation programmes were similar to previous results for these programmes in housed dairy heifers in North America (Ambrose et al. 2008; Stevenson et al. 2008; Colazo and Ambrose 2011). For the GPG+P4 group, the results were marginally lower than 57% conception rate reported by McDougall et al. (2013). The 52.4% conception rate seen in this study is very similar to the 53% reported by Pickering (2008) across 10 commercial dairy herds in New Zealand. In that survey heifers were synchronised using a GPG+P4 programme and inseminated on Day 10 or on detection of oestrus. Comparing the drug costs of the GPG+P4 and the P4+PGF protocols, the latter was considerably less expensive. As of July 2013, the costs of the products used were NZ$20.02 for the P4-releasing intravaginal device, NZ$2.04/mL for the cloprostenol and NZ $5.60/mL for the gonadorelin. Therefore the total cost for the GPG+P4 protocol was NZ$35.30 and for the P4+PGF protocol was NZ$24.10 per animal. Thus, assuming each programme resulted in a conception rate of 53.6% (the overall average seen in this study), the cost per pregnancy for GPG and P4 was NZ $65.85, whereas for the P4 and PGF treated animals it was NZ $44.96, a difference of more than $20. However, the GPG+P4 programme required only 3 days of yardings and manipulations, whereas the P4+PGF programme required four, which would clearly add to overall costs. However for a group of 84 heifers (the average number of heifers treated per farm in this study), the difference in drug cost between synchronising the heifers using GPG and P4, rather than P4 and PGF, would be NZ $940, a difference that is likely to be considerably more than the cost of an extra yarding. The financial advantage of using P4 and PGF, rather than GPG and P4, would still remain, even if the odds of pregnancy after treatment with GPG and P4 were at the top end of the 95% CI (0.67– 1.23) found in this study; i.e. if the odds of pregnancy after GPG and P4 were 1.23 times higher than those after treatment with P4 and PGF. Assuming a 53% conception rate after the P4+PGF protocol, an OR of 1.23 would indicate a true conception rate after the GPG+P4 protocol of 58.1%. This would result in the cost per pregnancy for the P4+PGF programme being NZ$45.60 and that for GPG+P4 being NZ$60.75, a

difference of NZ$15. We thus believe that our assessment that the P4+PGF is a more cost effective programme for synchronising heifers under New Zealand conditions than GPG +P4 is a robust one, but also that further research with a specific economic focus is required to more accurately establish this benefit. Nevertheless, cost is not the only important criterion, the convenience of the three yardings required for the GPG+P4 programme may outweigh the cost benefit of the P4+PGF programme, but the simplicity of the latter has other advantages. There were double treatments on all treatment days during the GPG+P4 programme, but only single treatments with the P4+PGF programme. Under commercial conditions, multiple treatments at a single yarding may lead to a higher proportion of incorrect treatments, again favouring the use of P4 and PGF rather than GPG and P4. As expected, there were significant differences between farms in conception rates to the FTAI. There was no interaction between farm and treatment, so there was no evidence that the relative efficacy of the two programmes was related to the underlying fertility of the treated heifers. This study did not examine the benefits of synchrony compared with natural mating, but this lack of a significant interaction strongly suggests that the underlying fertility of the heifers will have more impact on whether synchronisation is economically beneficial (compared to natural mating) than whether to use a P4+PGF or GPG+P4 programme for synchronisation of oestrus. In conclusion, the results of this study suggest that heifers inseminated at a fixed-time after synchronisation of ovulation using a P4 +PGF programme had conception rates similar to those synchronised using a GPG+P4 programme, and the cost of drugs used was considerably less. Further research is required to better establish the economic benefit of using the P4 and PGF programme, and to identify whether other programmes that are cheaper than a GPG+P4 programme, such as a removal of the first GnRH treatment, can result in similar conception rates to the two programmes tested in this study whilst retaining the major benefit of the GPG+P4 programme used in this study (i.e. only three yardings).

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Acknowledgements This research was supported by New Zealand International Doctoral Research scholarship and Massey University Doctoral Research Scholarship. Statistical advice from Professor Nicolas Lopez–Villalobos and product provision by Bomac Laboratories is gratefully acknowledged. The contribution of the dairy farmers and farm managers of the Manawatu region is also acknowledged.

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*Macmillan KL. Reproductive management of dairy cattle. In: Fielden ED, Smith JF (eds). Reproductive Management of Grazing Ruminants in New Zealand, Occasional Publication 12. Pp 91–112. Society of Animal Production, Hamilton, NZ, 1998 McDougall S, Rhodes FM, Compton CWR. Evaluation of three synchrony programs for pasture-based dairy heifers. Theriogenology 79, 882–9, 2013 Parker KI, Compton CWR, Anniss FM, Weir AM, McDougall S. Management of dairy heifers and its relationships with the incidence of clinical mastitis. New Zealand Veterinary Journal 55, 208–16, 2007 Peeler ID, Nebel RL, Pearson RE, Swecker WS, Garcia A. Pregnancy rates after timed AI of heifers following removal of intravaginal progesterone inserts. Journal of Dairy Science 87, 2868–73, 2004 *Pickering J. AI synchrony in dairy heifers. Proceedings of the Society of Sheep and Beef Cattle Veterinarians of the New Zealand Veterinary Association. Pp 183– 9, 2008 Rivera H, Lopez H, Fricke PM. Fertility of Holstein dairy heifers after synchronization of ovulation and timed AI or AI after removed tail chalk. Journal of Dairy Science 87, 2051, 2004 Smith RD, Pomerantz AJ, Beal WE, McCann JP, Pilbeam TE, Hansel W. Insemination of holstein heifers at a preset time after estrous cycle synchronization using progesterone and prostaglandin. Journal of Animal Science 58, 792– 800, 1984 Stevenson JL, Dalton JC, Santos JEP, Sartori R, Ahmadzadeh A, Chebel RC. Effect of synchronization protocols on follicular development and estradiol and progesterone concentrations of dairy heifers. Journal of Dairy Science 91, 3045–56, 2008 Xu ZZ, Burton LJ. Effects of oestrus synchronisation and fixed-time artificial insemination on the reproductive performance of dairy heifers. New Zealand Veterinary Journal 47, 101–4, 1999a Xu ZZ, Burton LJ. Reproductive performance of dairy heifers after estrus synchronization and fixed-time artificial insemination. Journal of Dairy Science 82, 910–7, 1999b

Submitted 10 April 2014 Accepted for publication 23 October 2014 First published online 30 October 2014

*Non-peer-reviewed

Conception rates to fixed-time artificial insemination of two oestrus synchronisation programmes in dairy heifers.

To evaluate the conception rate to fixed-time artificial insemination (FTAI) of two oestrus synchronisation programmes in dairy heifers on eight farms...
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