Heifers with positive genetic merit for fertility traits reach puberty earlier and have a greater pregnancy rate than heifers with negative genetic merit for fertility traits

Abstract

This study investigated the hypothesis that dairy heifers divergent in genetic merit for fertility traits differ in the age of puberty and reproductive performance. New Zealand's fertility breeding value (FertBV) is the proportion of a sire's daughters expected to calve in the first 42 d of the seasonal calving period. We used the New Zealand national dairy database to identify and select Holstein-Friesian dams with either positive (POS, +5 FertBV, n = 1,334) or negative FertBV (NEG, −5% FertBV, n = 1,662) for insemination with semen from POS or NEG FertBV sires, respectively. The resulting POS and NEG heifers were predicted to have a difference in average FertBV of 10 percentage points. We enrolled 640 heifer calves (POS, n = 324; NEG, n = 316) at 9 d ± 5.4 d (± standard deviation; SD) for the POS calves and 8 d ± 4.4 d old for the NEG calves. Of these, 275 POS and 248 NEG heifers were DNA parent verified and retained for further study. The average FertBV was +5.0% (SD = 0.74) and −5.1% (SD = 1.36) for POS and NEG groups, respectively. Heifers were reared at 2 successive facilities as follows: (1) calf rearing (enrollment to ~13 wk of age) and (2) grazier, after 13 wk until 22 mo of age. All heifers wore a collar with an activity sensor to monitor estrus events starting at 8 mo of age, and we collected weekly blood samples when individual heifers reached 190 kg of body weight (BW) to measure plasma progesterone concentrations. Puberty was characterized by plasma progesterone concentrations >1 ng/mL in at least 2 of 3 successive weeks. Date of puberty was defined when the first of these samples was >1 ng/mL. Heifers were seasonally bred for 98 d starting at ~14 mo of age. Transrectal ultrasound was used to confirm pregnancy and combined with activity data to estimate breeding and pregnancy dates. We measured BW every 2 wk, and body condition and stature at 6, 9, 12, and 15 mo of age. The significant FertBV by day interaction for BW was such that the NEG heifers had increasingly greater BW with age. This difference was mirrored with the significant FertBV by month interaction for average daily gain, with the NEG heifers having a greater average daily gain between 9 and 18 mo of age. There was no difference in heifer stature between the POS and NEG heifers. The POS heifers were younger and lighter at puberty, and were at a lesser mature BW, compared with the NEG heifers. As a result, 94 ± 1.6% of the POS and 82 ± 3.2% of the NEG heifers had reached puberty at the start of breeding. The POS heifers were 20% and 11% more likely to be pregnant after 21 d and 42 d of breeding than NEG heifers (relative risk = 1.20, 95% confidence interval of 1.03-1.34; relative risk = 1.11, 95% confidence interval of 1.01-1.16). Results from this experiment support an association between extremes in genetic merit for fertility base on cow traits and heifer reproduction. Our results indicate that heifer puberty and pregnancy rates are affected by genetic merit for fertility traits, and these may be useful phenotypes for genetic selection.

Investigating anogenital distance and antral follicle count as novel markers of fertility within a herd of cows with positive or negative genetic merit for fertility traits

“…The New Zealand Fertility Breeding Value (FertBV) was used to create cows with positive (POS; +5%) or negative (NEG; −5%) genetic merit for fertility traits. At the same time, limits were put on the inbreeding coefficient of the offspring (<12%) and the expected parent averages for milk volume, fat, protein, BW, and ancestry (% North American Holstein-Friesian) to ensure groups were within 1 standard deviation and calves were >15/16 parts Holstein-Friesian as described in Meier et al (2021a). These calves were followed for over 3 yr to determine influences of the FertBV on puberty (Meier et al, 2021a) and other reproductive phenotypes (Meier et al, 2021b; Figure 1).…”

“…Full details of the heifer breeding are described in Meier et al, (2021a). In brief, weekly plasma sampling for progesterone analysis started when heifers were approximately 190 kg and continued until puberty was reached.…”

“…Our team has generated a custom-bred herd of Holstein-Friesian dairy cattle with positive or negative genetic merit for fertility traits as a resource and has followed them from birth through to their third pregnancy (Meier et al, 2021a;2021b). We hypothesized that the genetic merit for fertility traits would be associated with AFC and AGD; therefore, we investigated these phenotypes in our fertility research herd.…”

Changes in plasma electrolytes, minerals, and hepatic markers of health across the transition period in dairy cows divergent in genetic merit for fertility traits and postpartum anovulatory intervals

“…An alternative model was recently established by Meier et al (2021a,b) using a 500-cow study population divergent in genetic merit for fertility traits based on the New Zealand fertility breeding value (FertBV). The goal was to establish an animal model only divergent in FertBV, by limiting differences in breeding values for BCS, BW, and milk production traits (Meier et al, 2021b). Approximately half the study cows were custom bred to be positive (+5%; POS) and half negative (−5%; NEG) for FertBV.…”

“…Greater circulating concentrations of aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT) have also been reported in cows that had not ovulated by 3 wk postcalving compared with those that had (Kawashima et al, 2016), supporting an important role of liver function in the resumption of estrous. Our studies involved cows that differed in their FertBV as indicated minor BCS differences over the transition period, but there was a wide range of PPAI, especially in NEG cows (Meier et al, 2021b). Therefore, we hypothesized that blood metabolite, minerals and metabolic stress marker profiles during the transition period would be similar among the POS and NEG cows, but may be associated with duration of PPAI.…”