Thermoregulation in neonatal calves is essential to maintain body temperature. Especially during the cold season, a successful metabolic adaptation is required to avoid health and production losses. Colostrum and transition milk are characterized by an elevated fat content compared with mature milk. Although colostral fat content is known to vary considerably among cows, its specific effect on postnatal metabolic adaptation in calves under cold conditions has not been well characterized. The objective of the present study was to investigate the impact of a different fat content in colostrum and transition milk on metabolic adaptation in newborn calves during the cold season. Twelve calves (n = 9 Holstein, n = 3 Holstein × Limousin crossbred; birth weight 41.3 ± 1.8 kg) born to cows without dystocia were enrolled immediately after birth and studied until d 21 postpartum (p.p.). The experimental period lasted from February to March 2025. Based on sex, birth weight, and breed, calves were assigned to either a group receiving 2.5 L full-fat colostrum (FF; n = 6; 4.81% fat) or low-fat colostrum (LF; n = 6; 0.58% fat) at 4 and 12 h p.p. Both FF and LF derived from the same pool of colostrum and differed only in fat content. On d 2 and 3 p.p., FF and LF received transition milk (300 mL colostrum of different fat content mixed with 2.7 L bulk tank milk). From d 4 onwards, all calves were fed identically with bulk tank milk. Blood was sampled from d 2 to 7 and analyzed for various endocrine and metabolic parameters (e.g., glucose [GLU], insulin, cortisol, glucagon, nonesterified fatty acids [NEFA], triglycerides [TG], total cholesterol [TC], high-density lipoprotein cholesterol [HDL-C]), low-density lipoprotein cholesterol [LDL-C], very low-density lipoprotein cholesterol [VLDL-C], aspartate aminotransferase [ASAT], gamma-glutamyl transferase [GGT], triiodothyronine, thyroxine, total protein [TP], and IgG). Plasma GLU concentration increased during the first days after parturition in both LF and FF, with greater concentrations in FF during the first 4 d p.p. Serum concentrations of TG, TC, HDL-C, and VLDL-C were greater in FF until d 4 p.p., and TC and LDL-C were greater in FF compared with LF from d 5 to 21. No differences were observed for serum IgG, insulin, NEFA, and TP. Cortisol and glucagon concentrations as well as activity of GGT were elevated in LF compared with FF until d 4 of age. In conclusion, the present study showed that the fat content of colostrum and transition milk affected metabolic adaptation in neonatal calves during the first days of life. The overall lower energy availability in LF was reflected by changes of parameters related to glucose and lipid metabolism. Further studies investigating the impact of colostral fat content under different environmental conditions are warranted.

Insulin-like growth factors (IGFs) are essential for oocyte maturation. Their bioavailability is regulated by their respective binding proteins (IGFBPs) and proteases. IGFBP-4 blocks the biological effects of IGFs. High IGFBP-4 expression has been associated with follicle atresia. We hypothesized that IGFBP-4 affects oocyte developmental competence during maturation. Therefore, the aim of this study was to examine the effect of IGFBP-4 on the developmental rate of bovine cumulus–oocyte complexes (COCs) during in vitro embryo production. Abattoir-derived COCs were matured with rbIGFBP-4 (2000, 540, and 54 ng/mL) compared to a control. Cumulus expansion, oocyte maturation, cleavage, blastocyst, and hatching rates were evaluated. Furthermore, blastocyst gene expression of SOCS2, STAT3, SLC2A1, SLCA3, BAX, and POU5F1 transcripts were quantified using RT-qPCR. No statistical differences were detected among the groups for cumulus expansion, maturation, cleavage, blastocyst rates, or all gene transcripts analyzed. However, at day 8 and 9, the number of total hatching and successfully hatched blastocysts was lower in 2000 ng/mL rbIGFBP-4 compared to the control (day 8: total hatching: 17.1 ± 0.21 vs. 31.2 ± 0.11%, p = 0.02 and hatched blastocyst 6.7 ± 0.31 vs. 21.5 ± 0.14%, p = 0.004; day 9 total hatching 36.4 ± 0.18 vs. 57.7 ± 0.10%, p = 0.009 and hatched blastocyst 18.2 ± 0.21 vs. 38.1 ± 0.11%, p = 0.004). We concluded that high concentrations of rbIGFBP-4 might negatively affect the subsequent ability of the embryo to hatch and possibly compromise further elongation.