Phenotypic relationships between the interval from calving to first luteal activity and fertility in a seasonal dairy production system

Estrous activity in lactating cows with divergent genetic merit for fertility traits

This observational study aimed to determine the effect of genetic merit for fertility traits on estrous expression and estrous cycle duration in grazing dairy cows, as measured by an activity monitoring device. A secondary aim was to describe changes in expression of estrus that occur during successive estrous cycles postpartum. Neck-mounted, activity-monitoring devices (Heatime, SCR Engineers Ltd.) were fitted to nulliparous Holstein-Friesian heifers with positive (POS FertBV) or negative genetic merit for fertility traits (NEG FertBV) to capture activity data during their first and second lactations (POS FertBV: n = 242, n = 188; NEG FertBV: n = 159, n = 87 in lactation 1 and 2, respectively). An estrous event was identified when the activity change index exceeded 26 activity units (AU) for 4 h. A total of 1,254 and 892 estrous events were identified in lactation 1 and 2, respectively. Estrous duration was defined as the interval between when the threshold was first exceeded and when activity dropped below the threshold, with no new event starting within 24 h of the end of the previous event. This definition of estrus included cows in which activity crossed the threshold multiple times in a day and were classified as a single estrous event. A second measure, high activity duration, was defined as the total hours that activity exceeded the threshold. To characterize estrous activity, peak activity (above baseline) and total activity (area under the curve of activity above baseline) were measured. Compared with NEG FertBV cows, POS FertBV cows had more active, longer estrous events. In lactation 1, the POS FertBV group had a mean estrous duration and a high activity duration of 12.5 and 12.4 h compared with 11.4 and 11.3 h for the NEG FertBV group [standard error of the difference (SED) = 0.5 and 0.4 h, respectively]. This significant difference also occurred in lactation 2, with a mean estrous duration of 13.1 versus 11.8 h (SED = 0.5 h) and a high activity duration of 13.0 versus 11.8 h (SED = 0.4 h) in the POS and NEG FertBV groups, respectively. Total activity and peak activity were greater in the POS compared with the NEG FertBV group in lactation 1 (peak activity: 65.5 vs. 55.8 AU, SED = 2.4 AU; total activity: 588 vs. 494 AU, SED = 25 AU) and lactation 2 (peak activity: 72.5 vs. 61.2 AU, SED = 2.9 AU; total activity: 648 vs. 541 AU, SED = 30 AU). Estrous cycle duration did not differ between the POS and NEG FertBV groups (lactation 1: 20.4 vs. 20.6 d, SED = 0.25; lactation 2: 20.8 vs. 21.0 d, SED = 0.28). Less estrous activity of the cow was associated with the first postpartum estrus. In contrast, the number of previous estrous events did not consistently affect the duration of the subsequent estrous cycle. The outcomes of this study provide evidence that positive genetic merit for fertility traits is associated with more overt estrous expression. Selection for these traits may improve estrous expression and thus estrous detection in commercial herds.

Increasing conception rate by addition of a second prostaglandin injection in an Ovsynch and progesterone treatment programme for dairy cows not detected in oestrus before the start of the seasonal mating period

AIMS

To assess the effect on conception rate to first service, 3- and 6-week in-calf rates, final pregnancy rate and the hazard of pregnancy, of addition of a second prostaglandin (PG) injection 24 hours after the first, in a synchrony programme combining Ovsynch and progesterone in pasture-based dairy cows that had not been detected in oestrus before the start of the seasonal mating period.

METHODS

This prospective, negative-controlled study was conducted using anoestrous cows (n = 1,411) from nine spring-calving dairy herds in the Waikato region of New Zealand. Ovaries of cows not detected in oestrus were examined by transrectal ultrasonography and the presence of a corpus luteum determined. All cows were then treated with an intravaginal progesterone-releasing device and injected I/M with gonadorelin (Day -9). Cows were injected I/M with cloprostenol at device removal (Day -2) and on Day -1 were injected with either water (single PG; n = 720), or cloprostenol (double PG; n = 692). On Day 0 cows were injected again with gonadorelin, unless previously detected in oestrus, and were inseminated on Day 1. Based on dated pregnancy diagnosis by transrectal ultrasonography, cows were categorised as conceiving to first insemination, becoming pregnant in the first 3 or 6 weeks, or becoming pregnant by the end of the mating period.

RESULTS

Cows in the double PG group had increased conception rate to first service (45.3 (95% CI = 45.1-45.4)% vs. 41.1 (95% CI = 41.0-41.3)%; p < 0.001), 3-week in-calf rate (53.4 (95% CI = 53.6-54.0)% vs. 49.2 (95% CI = 49.0-49.4)%; p < 0.001), and 6-week in-calf rate (67.2 (95% CI = 65.7-68.8)% vs. 63.5 (95% CI = 62.0-65.0)%; p = 0.014) compared to cows in the single PG group. Final pregnancy rate and hazard of pregnancy did not differ between treatment groups (p >0.2).

CONCLUSIONS

Addition of a second PG injection 24 hours after the first, increased conception rate to first service and the proportion of cows pregnant by 3 and 6 weeks after commencement of the mating period.

CLINICAL RELEVANCE

Improved outcomes can be achieved when treating those cows not detected in oestrus by the start of the seasonal mating period by addition of a second PG injection to the currently recommended treatment protocol for these animals.

Novel approaches to genetic analysis of fertility traits in New Zealand dairy cattle

The fertility of dairy cattle in New Zealand is well below industry targets, and the current New Zealand fertility breeding value (BV) could potentially be improved using additional information and traits. Data from 169 herds were analyzed to determine the benefits of using alternative phenotypic measures in the calculation of the fertility BV. The heritability of calving season day (CSD; calving season day as an integer day of the year) and the probability of an animal calving within 42 d of the planned start of calving (CR42) increased modestly (from 0.0206 to 0.0213 and 0.0087 to 0.0092, respectively) after accounting for the use of intravaginal progesterone-releasing devices for treatment of anestrous cows (anestrum treatment) and induced calvings. Incidence of either anestrum treatment or calving induction as a single binomial trait (AT/IND) had a heritability of 0.0223 and showed moderate genetic correlation with the probability of an animal being mated within 21 d of the planned start of mating (PM21; -0.4473), but much higher with CSD (0.8445). The use of pregnancy diagnosis data allowed fertility information that would otherwise be discarded to be included in analyses; when used to assign a prolonged CSD and a value of 0 for CR42 to animals that failed to calve, it increased the heritabilities of both of these traits (to 0.0278 and 0.0114, respectively). Because CSD was found to be more than twice as heritable as its binary counterpart, it shows potential to replace CR42 as the calving trait used in the fertility BV. Postpartum anestrous interval (PPAI), derived using incomplete premating estrous recording in some herds, had a heritability of 0.0813 and hence has potential as a trait to be included in genetic improvement programs but would require more rigorous recording of estrous during the premating period to be an effective trait. Based on selection index theory, the modifications made to current selection criteria using novel fertility traits increased the accuracy of prediction of fertility merit by more than 12%. Because of the increasing economic importance of fertility traits, and low heritabilities requiring large numbers of recorded daughters to get accurate fertility BV predictions on sires, data recorded on farm will become increasingly important in the genetic improvement of fertility.

Ovarian activity in Fleckvieh, Brown Swiss and two strains of Holstein-Friesian cows in pasture-based, seasonal calving dairy systems

The objectives of the study were to compare the ovarian activity of Holstein-Friesian (CH HF), Fleckvieh (CH FV) and Brown Swiss (CH BS) dairy cows of Swiss origin with that of Holstein-Friesian (NZ HF) dairy cows of New Zealand origin, the latter being used as a reference for reproductive performance in pasture-based seasonal calving systems. Fifty, second-lactation NZ HF cows were each paired with a second-lactation Swiss cow (17, 15 and 18 CH HF, CH FV and CH BS respectively) in 13 pasture-based, seasonal-calving commercial dairy farms in Switzerland. Ovarian activity was monitored by progesterone profiling from calving to first breeding service. CH BS cows produced less energy-corrected milk (mean 22·8 kg/d) than the other breeds (26·0–26·5 kg/d) during the first 100 d of lactation. CH HF cows had the lowest body condition score (BCS) at calving and the greatest BCS loss from calving to 30 d post partum. Commencement of luteal activity (CLA) was later for NZ HF than for CH FV (51·5 v. 29·2 d; P <0·01), with CH HF and CH BS intermediate (43 d). On average, NZ HF and CH HF cows had one oestrous cycle before the onset of the seasonal breeding period; this was less (P<0·01) than either CH FV (1·7) or CH BS (1·6). There was a low prevalence of luteal persistency (3%) among the studied cows. First and second oestrous cycle inter-ovulatory intervals did not differ between breeds (20·5–22·6 d). The luteal phase length of CH BS during the second cycle was shorter (10·6 d) than that of the other breeds (13·8–16·0 d), but the inter-luteal interval was longer (9·8 d v. 7·0–8·0 d). The results suggest that the Swiss breeds investigated have a shorter interval from calving to CLA than NZ HF cows.

A comparison of three strains of holstein-friesian grazed on pasture and managed under different feed allowances

This experiment compared Holstein-Friesian (HF) cows of New Zealand (NZ) origin representative of genetics present in the 1970s (NZ70; n = 45) and 1990s (NZ90; n = 60), and a group of HF cows of North American origin with 1990s genetics (NA90; n = 60), which were managed in grazing systems with a range of feeding allowances (4.5 to 7.0 t/cow per yr) over 3 yr. The NZ70 cows had the lowest Breeding Worth genetic index and the lowest breeding values for yields of fat, protein, and milk volume; the NZ90 and NA90 cows were selected to have similar breeding values for milk traits and were representative of cows of high genetic merit in the 1990s. The NZ90 cows had a higher milk protein concentration (3.71%) than either the NA90 (3.43%) or the NZ70 cows (3.41%), and a higher milk fat concentration (4.86%) than the NA90 cows (4.26%) with a level similar to the NZ70 cows (4.65%). The NZ90 cows produced significantly greater yields of fat, protein, and lactose than the NA90 and NZ70 cows. The NZ70 cows had the lowest mean annual body weight (473 kg) but the highest body condition score (BCS; 5.06). Days in milk were the same for the 2 NZ strains (286 d in milk), both of which were greater than the NA90 cows (252 d in milk). There was no genotype x environment interaction for combined milk fat and protein yield (milksolids), with NZ90 producing 52 kg/cow more than the NA90 at all feeding levels. The NZ70 strain had the highest seasonal average BCS (5.06), followed by the NZ90 (4.51) and the NA90 (4.13) strains on a 1 to 10 scale. Body condition score increased with higher feeding levels in the 2 NZ strains, but not in the NA strain. The first-parity cows commenced luteal activity 11 d later than older cows (parities 2 and 3), and the NA90 cows commenced luteal activity 4 and 10 d earlier than the NZ70 and NZ90 cows. Earlier estrus activity did not result in a higher in-calf rate. The NZ70 and NZ90 cows had similar in-calf rates (pregnancy diagnosed to 6 wk; 69%), which were higher than those achieved by NA90 cows (54%). Results showed that the NA90 strain used in this experiment was not suitable for traditional NZ grazing systems. Grazing systems need to be modified if the NA90 strain is to be successfully farmed in NZ. The data reported here show that the NA90 cows require large amounts of feed, but this will not prevent them from having a lower BCS than the NZ strains. Combined with poor reproductive performance, this means that NA90 cows are less productive than NZ HF in pasture-based seasonal calving systems with low levels of supplementation.

Characterization of biological types of cattle (Cycle VII): Influence of postpartum interval and estrous cycle length on fertility12

Genetic improvement in reproductive efficiency through selection is difficult because many reproductive traits are binomial and have low heritabilities. Before genetic markers can be generated for fertility in cows, greater characterization of reproductive phenotypes is needed to understand the components of the trait. The current study tested the hypotheses that: 1) breeds vary in postpartum interval to estrus (PPIE) and estrous cycle length, 2) a longer estrous cycle immediately before breeding increased pregnancy rates, and 3) a greater number of cycles before breeding increased conception rates. The postpartum interval to estrus, estrous cycle length, and number of cycles before breeding were examined in F1 cows (n = 519) obtained from mating Hereford, Angus, and MARC III cows to Hereford, Angus, Simmental, Limousin, Charolais, Gelbvieh, and Red Angus sires. Cows were classified as having 0, 1, 2, or 3 observed estrous cycles before breeding. All traits analyzed were adjusted to constant BCS. Sire breed of the cow influenced length of the PPIE and number of cycles before the start of breeding (P <0.001). Simmental-sired cows had the shortest PPIE and greatest number of cycles before breeding, whereas Limousin-sired cows had the longest PPIE and least number of cycles before breeding. Cows with a greater number of cycles before breeding did not have greater conception rates than cows that had not exhibited standing estrus before breeding (P = 0.87). In cows that cycled before breeding, the length of the estrous cycle immediately before breeding was influenced by dam breed and BCS (P <0.01). Cows out of Hereford dams had shorter estrous cycles than cows out of MARC III or Angus dams, and estrous cycle length increased as BCS increased. Conception rate decreased as length of the estrous cycle immediately before breeding increased (P = 0.05, -2.2% per d of cycle length). Therefore, previously anestrous cows were just as likely to conceive as cows that had cycled before breeding, and an increased number of observed estrous cycles before breeding did not increase conception rates. There may be an influence of the length of estrous cycle immediately before breeding on conception rates, possibly because a longer estrous cycle results in a persistent follicle with greater potential for a lower quality oocyte. Breed differences in PPIE and estrous cycle length suggest that there are genetic components to these traits.