A combination of nutrition and genetics is able to reduce age at puberty in Nelore heifers to below 18 months

Abstract

Nelore heifers usually begin their reproductive life at ⩾24 months of age mainly due to suboptimal nutritional conditions and genetics. This study aimed to determine the effect of expected progeny difference (EPD) for age at first calving and average daily gain (ADG) on puberty in Nelore (Bos taurus indicus) heifers. A total of 58 weaned heifers (initial BW=174±6 kg; age=9±1 months) were allocated into 28 feedlot pens. Heifers were born from four sires, of which two had low EPD for age at first calving (L; n=33) and two had high EPD for age at first calving (H; n=25). Then, heifers of each EPD were randomly assigned to high ADG (HG; 0.7 kg) or low ADG (LG; 0.3 kg), resulting in four treatments: heifers from L sires were submitted to either HG (LHG; n=17) or LG (LLG; n=16), and heifers from H sires were submitted to either HG (HHG; n=12), or LG (HLG; n=13). The HG heifers were fed a 75% grain diet, whereas the LG heifers received 93% of forage in their diet. Blood samples were collected at 9, 14, 18, 24 and 28 months of age for IGF1 and leptin determination. There was a treatment effect (P<0.01) on the proportion of heifers that attained puberty by 18 (62%, 0%, 0% and 0%), 24 (100%, 6%, 54% and 0%) or 36 (100%, 100%, 100% and 38%) months of age for LHG, LLG, HHG and HLG treatments, respectively. In addition, mean age at puberty was different across treatments (P<0.01). Heifers from the LHG achieved puberty at the earliest age when compared with cohorts from other treatments (18.1, 28.9, 23.9 and 34.5 months for LHG, LLG, HHG and HLG, respectively). Serum IGF1 concentrations were higher for L heifers compared with H cohorts at 9, 14, 18, 24 and 28 months of age (P<0.01; treatment×age interaction), whereas circulating leptin concentrations were higher (P<0.01; age effect) as heifers became older, regardless of the treatments. In conclusion, only Nelore heifers with favorable genetic merit for age at first calving were able to attain puberty by 18 months of age. In heifers with unfavorable genetic merit for age at first calving, supplementary feeding to achieve high ADG was unable to shift the age at puberty below 24 months.

Genome-wide scan highlights the role of candidate genes on phenotypic plasticity for age at first calving in Nellore heifers

“…4 and Supplementary Table S4). Such findings support the hypothesis that production systems on pasture conditions under Low EC level exhibit an important factor for delaying the precocity onset, through its impact on the concentration of circulating metabolites 18,36,41,42 .…”

“…The gene set identified in Low EC levels plays an important role to keep metabolic homeostasis, leading to different growth rates according to heifer adaptability allowing that precocious heifers reach their genetic potential. Ferraz Jr et al 18 observed that Nellore heifers selected to sexual precocity in the low nutritional level were able to attain the lowest age at puberty compared to heifers with high AFC, mainly by differences in IGF1 and Leptin hormone level. In Low EC, physiological changes affecting levels of insulin and glucose could affect the AFC, because the oocyte quality and development of both oocyte and embryo respond directly to these metabolic inputs 40,49 .…”

“…Hence, these genes can cause variation in AFC in Nellore heifers due to their influence on metabolic homeostasis, by direct action on the reproductive process, e.g. ovarian follicles, oocytes quality and embryos 18,49 . The genes USP21 and UFC1 are members of the Ubiquitin family gene and they were related to the metabolic process (GO:0008152), affecting the proteolysis regulating that represents a key aspect for the cellular function 63 .…”

“…In this framework, the EC descriptor used to encompass the production level was based on the best linear unbiased estimates (BLUE) solutions of the contemporary group for yearling body weight (YBW), once it condenses the different management and environmental factors in which the animals were raised. We focused on YBW because the differences in production environments affecting YBW present an important effect on heifers' early sexual puberty 2,3,17,18 .…”

Genomic reaction norm models exploiting genotype × environment interaction on sexual precocity indicator traits in Nellore cattle

“…However, sexual precocity in cattle is affected by many environmental factors, such as heat stress and nutrition, which play a major role in the age of onset of puberty (Robinson et al ). Differences in environments have been pointed out as the main issue for sexual precocity variation in Brazilian herds (Nepomuceno et al ; Ferraz et al ). Brazilian beef cattle are raised predominantly on pasture with a wide range of environmental conditions and seasonal variations in forage production and different nutritional levels.…”