CATTLE producers typically wean replacement heifers at seven months of age and raise them with limited nutritional input before their first breeding.
This managerial strategy is often associated with delayed puberty, particularly in tropically adapted Bos indicus-influenced cattle, according to researchers.
In Texas, the Bos indicus influence generally comes from Brahman genetics but can involve the Nelore breed as well.
To maximize successful pregnancies in replacement heifers early in their first breeding season, studies conducted at Texas A&M University and the Texas A&M AgriLife Research Station-Beeville are evaluating nutritional strategies to promote puberty consistently by 12-14 months of age in Bos taurus x Bos indicus crossbred heifers.
Drs. Marcel Amstalden and Gary Williams, reproductive physiologists at Texas A&M University and Texas A&M AgriLife Research, along with doctoral students Rodolfo Cardoso and Bruna Alves, are evaluating mechanisms that lead to the early onset of puberty in heifers. The goal of the work is to use newfound, fundamental knowledge of heifer development to optimize pregnancy in replacement heifers by 15 months of age and increase the proportion of heifers calving early in their first calving season.
"Nutrition plays an important role in the developmental controls of puberty in heifers," Williams said. "Breed type is a factor as well, and there are dietary strategies that can help us time the onset of puberty."
Recent research has shown that the age at puberty in Bos taurus beef heifers can be reduced to approximately nine months of age by early weaning calves at three to four months of age and feeding high-concentrate diets that promote increased rates of bodyweight gain for as few as 70 days, according to the researchers.
"A similar response is observed in heifers with Bos indicus influence," Williams said. "Our studies have indicated that early weaning, combined with elevated intake of high-concentrate diets, is associated with enhanced propionate production in the rumen and increased concentrations of the fat-derived hormone leptin in circulation."
"The brain is a major target for leptin's control of feed intake and energy expenditure," Amstalden said. "Because the impact of nutrition on age at puberty is largely mediated at the hypothalamus -- a region of the brain involved in the regulation of various body functions, including reproduction -- studies have focused on this brain region to explain the process of reproductive maturation."
Their studies found that a number of genes in the hypothalamus are regulated by nutrition and bodyweight gain during calfhood. Structural and functional changes in nerve cells are evident as well. The researchers are now testing management changes that would improve pregnancy rates early and optimize the lifetime productivity of replacement heifers.
However, they warned that strategies to accelerate puberty have to be considered with caution to avoid precocious puberty and unwanted pregnancies, which compromise heifer development and reproductive efficiency later in life.
Funding for the research is provided by the Texas Beef Enhancement Program through AgriLife Research and by the Agriculture & Food Research Initiative Competitive Grants program of the U.S. Department of Agriculture's National Institute of Food & Agriculture.
As metagenomic science advances, researchers are increasingly identifying the bacterial and viral populations of the rumen with greater detail.
At the recent midwestern section meetings of the American Society of Animal Science and American Dairy Science Assn., researchers from the University of Nebraska-Lincoln presented a few abstracts on the structure of ruminal microbial communities in feedlot cattle.
* In abstract O166, Nebraska researchers C. Anderson, M. Jolly, G. Erickson, T. Klopfenstein and S. Fernando noted that viruses are the most numerous biological entities on the planet, but little is known about their effects on rumen community structuring due to their size, rapid evolution and the fact that the majority cannot be cultured.
Using contemporary metagenomic approaches, the study of viral properties is now a possibility, which has helped with determining the influence viral populations have on complex environments such as the gut microbiome, Anderson et al. said.
To better understand the role and functional relationships of viruses, in particular how prophages influence rumen bacterial communities, Anderson et al. investigated viral and microbial relationships in four different diets using a metagenomic approach. In addition to the bacterial 16S gene, the viral and bacterial metagenomes were sequenced using 454-pyrosequencing to identify species composition, interactions between viruses and bacteria and metabolic profiles based on diet.
The researchers said their preliminary analysis demonstrated unclassified single-stranded DNA viruses dominating the rumen virome (49%). Of those single-stranded DNA viruses, Sclerotinia sclerotiorum hypovirulence-associated DNA virus-1 had the highest relative abundance (44.3%). Viral families present in the rumen included Germiniviridae (32%), Microviridae (12%), Circoviridae (5%), Nanoviridae (0.8%) and Inoviridae (0.09%).
According to Anderson et al., this is one of the few studies that analyzed the influence of diet on the structure of the rumen microbiome and virome and will help to improve the understanding of dynamics between viral and bacterial populations to improve cattle health, productivity and feed efficiency.
* In similar work, Nebraska researchers N.D. Aluthge, Y.A. Wanniarachchi, G.E. Erickson, T.J. Klopfenstein, B.L. Nuttelman, C.J. Schneider and S.C. Fernando discussed the effect of commensal microbial communities on the fecal shedding of Shiga toxin-producing Escherichia coli (STEC) in beef cattle (abstract O240).
Aluthge et al. noted that the main entry route of STEC into the environment is through cattle feces, and previous research has shown that the level and frequency of STEC shedding in cattle feces vary widely among individual animals.
In the current study, Aluthge et al. hypothesized that differences in beef animals' gut microbial community composition may play a role in their STEC shedding pattern. The researchers identified STEC high shedders and low shedders from among 170 beef steers over three time periods using selective microbiological culture methods and molecular methods.
Based on shedding numbers, 48 high shedders (greater than 104 STEC colony-forming units per gram of feces) and 48 low shedders (fewer than 102 colony-forming units per gram of feces) were selected for phenotyping for gut microbial composition using 16s rRNA-based amplicon sequencing, the researchers said.
Among the high shedders, Aluthge et al. reported, the prevalence of the seven major STEC serogroups was as follows: O157 (4.2%), O26 (4.2%), O111 (8.4%), O103 (12.5%), O121 (27.1%), O45 (18.8%) and O145 (91.7%), with more than one serogroup detected in 25% of animals.
According to the researchers, bio-informatic analyses of the sequences from high and low shedders revealed that members of the phylum Bacteroidetes were more abundant in the low shedders, while members of the phylum Proteobacteria were more abundant in the high-shedding animals. At the family level, Prevotellaceae were represented more in the low shedders than in the high shedders.
Aluthge et al. concluded that nine operational taxonomic units were significantly more abundant (P < 0.05) in low shedders than in high shedders.
Dr. John Wagner of Colorado State University presented a recent meta-analysis (abstract O241) showing that feeding a Saccharomyces cerevisiae fermentation product (SCFP) was positively associated with feedlot performance and quality grade.
Wagner compiled results from 28 feedlot studies for the meta-analysis, which evaluated the effects of the fermentation products on feedlot performance and carcass traits. Data consisted of 67 treatment means from 234 pens and 7,660 feedlot cattle.
Data were analyzed using mixed model procedures. Fixed class variables (no = 0 and yes = 1) included SCFP (Diamond V Original Product), monensin, tylosin and implants, as well as gender. Days on feed were included in models as a fixed continuous variable when significant (P < 0.05). "Study" was included in all models as a random class variable. The analysis was weighted by pen replicates per treatment mean.
Wagner said the meta-analysis found that cattle fed SCFP had 2.8 kg heavier (P < 0.10) final bodyweight, achieved greater (P < 0.01) average daily gain (ADG) of 1.42 kg versus 1.38 kg per day and gained 3.0% more (P < 0.01) weight per kilogram of dry matter intake (gain:feed ratio) versus control cattle. Dry matter intake was similar (P = 0.81) between control and SCFP groups.
Eleven studies were suitable for an analysis of receiving period data (31 records, 104 pens and 1,066 cattle). For SCFP versus control, Wagner found trends for increased (P = 0.11) final bodyweight of 1.2 kg, increased ADG of 1.27 kg versus 1.21 kg per day (P <0.08) and improved gain:feed of 4.4% (P = 0.11). Daily dry matter intake was not influenced (P = 0.78) by SCFP supplementation.
For the finishing period (28 records, 108 pens and 1,906 cattle), Wagner reported a trend (P < 0.14) for a 2.5% improvement in gain:feed for SCFP versus control, but the other performance differences were not significant (P > 0.20).
However, Wagner said an analysis of carcass data revealed an increase in percent Choice and Prime combined -- 66.5% versus 54.8% (P < 0.01) -- and a reduction in percent Select carcasses of 28.7% versus 40.9% (P < 0.05) for SCFP versus control; remaining carcass differences were not significant (P > 0.20).
Wagner concluded that the current meta-analysis indicates a beneficial effect of SCFP on ADG, feed efficiency and carcass quality grade when fed throughout the entire feeding period.