Reducing enteric methane (CH 4 ) production and improving feed conversion efficiency of dairy cows is of high importance. Residual feed intake (RFI) is one measure of feed efficiency, with low RFI animals being more efficient in feed conversion. Enteric CH 4 is an important source of digestible energy loss in ruminants and, because research in beef cattle has reported a positive relationship between RFI and daily CH 4 production, we hypothesized that low RFI dairy heifers, which are more feed efficient, would produce less CH 4 /d. We measured the daily methane production (g of CH 4 /d), methane yield [g of CH 4 /kg of dry matter intake (DMI)], and CH 4 per kilogram of body weight (BW) gain for 56 heifers (20-22 mo old) in a 2 × 2 factorial arrangement: factors included 2 breeds (Holstein-Friesian and Jersey; n = 28/breed), with equal numbers of animals previously determined as being either high [+2.0 kg of dry matter (DM)/d] or low RFI (−2.1 kg of DM/d; n = 28/RFI category). All heifers were commingled and offered unrestricted access to the same diet of dried alfalfa cubes. Between RFI categories, heifers did not differ in BW or BW gain but low RFI heifers had 9.3 and 10.6% lower DMI and DMI/kg of BW, respectively, than high RFI heifers. Similarly, RFI category did not affect CH 4 /d or CH 4 /kg of BWg, but CH 4 /kg of DMI was higher in low RFI heifers because of their lower DMI. These results might reflect more complete digestion of ingested feed in the more efficient, low RFI heifers, consistent with previous reports of greater apparent digestibility of organic matter. Holstein-Friesian heifers were heavier and consumed more total DM than Jersey heifers, but breed did not affect DMI/kg of BW or BWg. Jersey heifers produced less CH 4 /d, but not CH 4 /kg of DMI or CH 4 /kg of BWg. We detected no interaction between breed and RFI category in any of the variables measured. In conclusion, differences in RFI in dairy heifers did not affect daily CH 4 production (g/d); however, low RFI heifers had a greater CH 4 yield (g/kg of DMI) on a high forage diet.

Previous research has identified that Holstein-Friesian dairy heifers with positive (POS) genetic merit for fertility traits (FertBV) reach puberty earlier than heifers with negative (NEG) FertBV. The hypothalamuspituitary-gonadal (HPG) axis is functional in heifers before the onset of puberty, with increased LH release evident as heifers progress toward puberty. We investigated the functionality of the HPG axis in peripubertal Holstein-Friesian dairy heifers with divergent POS or NEG FertBV, hypothesizing that the earlier puberty onset of POS heifers is associated with earlier activation of the HPG axis than in NEG heifers. In experiment 1, we tested the dose responsiveness of POS heifers to an intravenous injection of either kisspeptin [Kiss; 2, 4, or 8 µg/kg of body weight (BW); n = 3 per dose] or a GnRH agonist (buserelin; 5, 10, or 20 ng/kg of BW; n = 3 per dose). The use of these 2 agonists investigates the status of the HPG axis in both the hypothalamus (Kiss) and pituitary (buserelin) glands. Doses of 4 µg/ kg BW of Kiss and 10 ng/kg BW of buserelin produced submaximal LH responses and were used in experiment 2, in which previously unused POS (n = 22) and NEG (n = 18) FertBV heifers were challenged with both agonists at 10 and 12 mo of age in a partial crossover design. Heifers were randomly allocated to treatment groups, balanced for age and BW. The LH response to buserelin was greater in POS heifers than NEG heifers at 10 mo of age, with no difference in response at 12 mo. The FSH response to buserelin and the LH and FSH responses to Kiss did not differ between the POS and NEG heifers at either age. These results indicate an association between divergent genetic merit for fertility and the LH release to buserelin at 10 mo of age, supporting the hypothesis that gonadotropin respon-siveness to a GnRH agonist is more advanced in POS heifers than in NEG heifers.

The greatest source of global anthropogenic methane (CH4) emissions is from ruminant livestock. Multiple mitigation strategies in livestock are currently being explored. Of these breeding for lower CH4 emitting ruminants has the advantage of being permanent and cumulative and universally applicable to all classes of livestock. Here, we show that methane emissions can be predicted by the complex community of microbiota sampled from rumens enabling evaluation of systems and individuals. Furthermore, there is evidence that the microbial community is controlled not only be the feed substrate but also by the host itself and that selecting hosts that favour a microbial fermentation with lowered methane emissions changes the energy source to the animal, and in turn both rumen physiology and body composition. Current methods for obtaining microbial DNA and subsequent sequencing of an animal’s microbiome, however, are too expensive to implement in commercial selection programs. A methodology that offers fast, low-cost, high throughput profiling of rumen microbiomes using Genotyping-by-sequencing (GBS) has been developed using an unbiased reference free approach to group microbiota. To date, this has been applied to over 4000 sheep samples and validated in cattle. Results show that microbial profiles are heritable and correlated with methane emissions and feed intake. This research is part of a flagship program funded by the global research alliance to disseminate global access to technologies that lower greenhouse gas emissions in ruminant livestock.

Fertility is determined to a significant extent by its underlying genetics and success of pregnancy is considered as a tool to define fertility. A substantial knowledge gap exists however, regarding epigenetic abnormalities resulting in infertility. The accuracy of information concerning fertility is critical to the success of an infertility treatment plan. Here, the authors explore the use and the value of blood plasma small extracellular vesicle (sEV) derived micro-RNA (miRNA) as biomarkers of fertility. Next-generation miRNA sequencing identified 14 differentially expressed (DE) miRNAs expressed with a substantial confidence between low fertile (LF) sEV and high fertile (HF) sEV (FDR < 0.05 and -logFC > 2), isolated from plasma of dairy cows (n = 10 per each HF and LF group). Interestingly, the majority of DE miRNAs were uniquely packaged into sEV and not found in circulating plasma. Validation using qRT-PCR miRNA assays indicated similar expression patterns of miR-17-5p, miR-2285dd, miR-2335, miR-12054 and miR-2285aw, and confirmed that miR-181b-5p was significantly upregulated in LF sEV (P value = 0.0093, Fold change = 2.665). The results from this study suggest that circulating sEV miRNA reflect the overall fertility status including the physiological status of the endometrium. Moreover, miR-181b-5p was validated as a prognostic sEV miRNA biomarker of fertility.