Fatty acid composition is a key factor affecting the flavor and quality of goat milk. CircRNAs are now recognized as important regulators of transcription, and they play an important role in the control of fatty acid synthesis. Thus, understanding the regulatory mechanisms controlling this process in ruminant mammary glands is of great significance. In the present study, mammary tissue from dairy goats during early lactation and the dry period (nonlactating) were collected and used for high-throughput sequencing. Compared to levels during the dry period, the expression level of circ003429 during early lactation was lower (12.68-fold downregulated). In isolated goat mammary epithelial cells, circ003429 inhibited the synthesis of triglycerides (TAG) and decreased the content of unsaturated fatty acids (C16:1, C18:1, and C18:2), indicating that this circRNA plays an important role in regulating lipid synthesis. A binding site for miR-199a-3p in the circ003429 sequence was detected, and a dual-luciferase reporter system revealed that circ003429 targets miR-199a-3p. Overexpression of circ003429 (pcDNA-circ003429) downregulated the abundance of miR-199a-3p. In contrast, overexpression of miR-199a-3p increased TAG content and decreased mRNA abundance of Yes-associated protein 1 (YAP1) (a target gene of miR-199a-3p), and TAG content was decreased and mRNA abundance was increased in response to overexpression of circ003429. These results indicate that circ003429 alleviates the inhibitory effect of miR-199a-3p on the mRNA abundance of YAP1 by binding miR-199a-3p, resulting in subsequent regulation of the synthesis of TAG and unsaturated fatty acids.

Making full use of feed nutrients, reducing energy losses and methane emissions, and maximizing production benefits have been ongoing goals of livestock production. Thirty-six healthy Dorper × Thin-tailed Han mutton ewes were divided into six groups using a completely randomized experimental design. A basal diet was provided to the control group, while the experimental group consumed a diet in which 15% was replaced by equal amounts of cottonseed meal (CM), rapeseed meal (RM), distillers dried grains with solubles (DDGS), soybean meal (SM), and fermented soybean meal (FSM). The study demonstrated that SM had the highest protein digestibility, followed by FSM, DDGS, and CM in that order. In terms of net energy, DDGS showed a significantly higher value compared to FSM (p < 0.05). Significantly higher abundances of Lactobacillaceae and Bifidobacteriaceae were observed in the CM group relative to the RM and FSM groups (p < 0.05). The methane emissions that we were most concerned about, whether it was daily emissions or metabolic weight basis, showed the same disparity between the groups, with the RM group having the most, followed in order by FSM, DDGS, and SM groups, and the least by the CM group. We found that the RM group had the highest relative abundance of Methanobrevibacter, followed by the FSM, SM, DDGS, and CM groups in that order, which is similar to the trend of methane emissions from each group. In summary, the highest apparent protein digestibility is SM, and the highest net energy value among these protein feeds is DDGS. RM will produce the most methane. In addition, the source of protein feed in the diet will affect the structural composition of rumen microorganisms.