In Brazil, the majority of dairy cattle are Holstein × Gyr (H×G). It is unknown whether excessive energy intake negatively affects their mammary development to the same extent as in purebred Holsteins. We hypothesized that mammary development of H×G heifers can be affected by dietary energy supply. We evaluated the effect of different average daily gains (ADG) achieved by feeding different amounts of a standard diet during the growing period on biometric measurements, development of mammary parenchyma (PAR) and mammary fat pad (MFP), and blood hormones. At the outset of this 84-d experiment, H×G heifers (n = 18) weighed 102.2 ± 3.4 kg and were 3 to 4 mo of age. Heifers were randomly assigned to 1 of 3 ADG programs using a completely randomized design. Treatments were high gain (HG; n = 6), where heifers were fed to gain 1 kg/d; low gain (LG; n = 6), where heifers were fed to gain 0.5 kg/d; and maintenance (MA; n = 6), where heifers were fed to gain a minimal amount of weight per day. Heifers were fed varying amounts of a single TMR to support desired BW gains. Over the 84 d, periodic biometric and blood hormone measurements were obtained. On d 84, all heifers were slaughtered and carcass and mammary samples were collected. At the end, HG heifers weighed the most (181 ± 7.5 kg), followed by LG (146 ± 7.5 kg) and MA (107 ± 7.5 kg) heifers. The ADG were near expected values and averaged 0.907, 0.500, and 0.105 ± 0.03 kg/d for HG, LG, and MA, respectively. In addition, body lengths, heart girths, and withers heights were affected by dietary treatment, with MA heifers generally being the smallest and HG heifers generally being the largest. Body condition scores differed by treatment and were highest in HG and lowest in MA heifers; in vivo subcutaneous fat thickness measurement and direct analysis of carcass composition supported this. The HG heifers had the heaviest MFP, followed by LG and then MA heifers. Amount of PAR was highest in LG heifers and was the same for HG and MA heifers. The percentage of udder mass occupied by PAR was lowest in HG heifers, differing from LG and MA heifers. Composition of MFP was not evaluated. Regarding PAR composition, no differences in ash or DM were found. On the other hand, CP concentration of PAR for HG heifers was lower than that for LG heifers, which was lower than that for MA heifers. Regarding the fat content, HG treatment was higher than LG and MA treatment, which did not differ from each other. In PAR, differences in relative abundance of genes related to both stimulation and inhibition of mammary growth were observed to depend on dietary treatment, sampling day, or both. The same can be said for most of the blood hormones that were measured in this experiment. In this experiment, high ADG achieved by feeding different amounts of a standard diet during the growing period negatively affected mammary development.

Nutrient requirements in cattle are dependent on physiological stage, breed and environmental conditions. In Holstein × Gyr crossbred dairy heifers, the lack of data remains a limiting factor for estimating energy and protein requirements. Thus, we aimed to estimate the energy and protein requirements of Holstein × Gyr crossbred heifers raised under tropical conditions. Twenty-two crossbred (½ Holstein × ½ Gyr) heifers with an average initial BW of 102.2 ± 3.4 kg and 3 to 4 months of age were used. To estimate requirements, the comparative slaughter technique was used: four animals were assigned to the reference group, slaughtered at the beginning of the experiment to estimate the initial empty BW (EBW) and composition of the animals that remained in the experiment. The remaining animals were randomized into three treatments based on targeted rates of BW gain: high (1.0 kg/day), low (0.5 kg/day) and close to maintenance (0.1 kg/day). At the end of the experiment, all animals were slaughtered to determine EBW, empty body gain (EBG) and body energy and protein contents. The linear regression parameters were estimated using PROC MIXED of SAS (version 9.4). Estimates of the parameters of non-linear regressions were adjusted through PROC NLIN of SAS using the Gauss–Newton method for parameter fit. The net requirements of energy for maintenance (NE m ) and metabolizable energy for maintenance (ME m ) were 0.303 and 0.469 MJ/EBW0.75 per day, respectively. The efficiency of use of ME m was 64.5%. The estimated equation to predict the net energy requirement for gain (NE g ) was: NE g (MJ/day) = 0.299 × EBW0.75 × EBG0.601. The efficiency of use of ME for gain (k g ) was 30.7%. The requirement of metabolizable protein for maintenance was 3.52 g/EBW0.75 per day. The equation to predict net protein requirement for gain (NP g ) was: NP g (g/day) = 243.65 × EBW−0.091 × EBG. The efficiency of use of metabolizable protein for gain (k) was 50.8%. We observed noteworthy differences when comparing to ME and protein requirements of Holstein × Gyr crossbred heifers with other systems. In addition, we also observed differences in estimates for NE m , NE g , NP g , k g and k. Therefore, we propose that the equations generated in the present study should be used to estimate energy and protein requirements for Holstein × Gyr crossbred dairy heifers raised in tropical conditions in the post-weaning phase up to 185 kg of BW.

The objective of this study was to evaluate the performance and health of Holstein calves fed low or high milk supply (MSP) with or without symbiotic complex (SYM) supplementation, consisting of prebiotics, probiotics, and fibrolytic enzymes. Thirty-two Holstein calves with body weight (BW) of 34 ± 7 kg were distributed in a randomized block design in a 2 × 2 factorial arrangement. Treatments consisted of low and high MSP: 10 % of BW from 1st to 8th weeks after birth (low) and 20 % BW from 1st and 2nd weeks after birth, 15 % BW for the 3rd and 4th weeks after birth, and 10 % BW from 5th and 8th weeks after birth (high). Solid ration was supplied in addition to milk. Intake, ADG, diet digestibility, and fecal consistency index were evaluated. Low and high MSP groups tended (P < 0.10) to differ in calf growth, final BW (69 vs. 73 kg), post-weaning average weight gain (548 vs. 788 g/day), and final average weight gain (549 vs. 646 g/day) in low and high MSP calves, respectively. There was an interaction between MSP level and SYM on the digestibilities of dry matter (DM) and neutral detergent fiber (NDF) (P < 0.10). In the low MSP group, inclusion of SYM increased digestibility of DM (0.720 to 0.736 g/kg) and NDF (0.758 to 0.783 g/kg). The inclusion of SYM improved calf health (P < 0.10) with a fecal score of 0.31 compared to 0.42 without SYM. Milk-feeding level was an important factor in calf performance, while SYM supplementation improved diet digestibility and animal health.

This study aimed to evaluate the effects of plane of nutrition and advancing days of pregnancy (DP) on maternal body composition and fetal development. Differing planes of nutrition were established by 2 feeding regimens (FR): ad libitum (AL) or maintenance (MA). Sixty-two nonlactating multiparous Holstein × Gyr cows with average body weight of 480 ± 10.1 kg and an age of 5 ± 0.5 yr were used. Cows were divided into 3 groups: pregnant (n = 44), nonpregnant (n = 12), and baseline reference cows (n = 6). The 56 pregnant and nonpregnant cows were randomly allocated into 2 different FR: AL or MA. Cows fed at MA received 1.15% of their body weight on a dry matter (DM) basis, receiving corn silage and a concentrate-based diet at a ratio of 93:7 on a DM basis. Reference group cows were slaughtered at the beginning of the experimental period to estimate body composition and empty body weight. To evaluate the effects of DP, pregnant and nonpregnant animals were slaughtered at d 140, 200, 240, and 270 of gestation. Feeding regimen affected maternal tissue composition. Days of pregnancy affected fresh weight (FW), DM, and energy content, but no differences were observed for crude protein (CP) and ether extract (EE) because of DP. Feeding regimen affected mammary gland components (CP, EE, and energy content), but not fresh or dry weights. Days of pregnancy influenced almost all mammary gland components except energy content. Regarding the uterus, FR affected only fresh and dry weights; however, DP affected every uterus component measured. The only interaction between FR and DP in this study was observed for placental FW. Cows fed AL on d 270 presented the same placental FW as cows at MA and AL on d 200 and 240. Further, pregnant cows fed at MA on d 270 had greater placental FW than cows fed AL at this day. Days of pregnancy, but not FR, influenced the composition of fetal fluids in pregnant cows. Finally, cows fed at MA had greater FW for the fetus than cows fed AL; however, fetus composition changed over DP. The FW, DM, EE, and energy content increased until d 270, but CP decreased. In conclusion, the novelty of our data presents how changes due to FR and DP occur in maternal tissues and the conceptus.

This study aimed to estimate energy requirements of pregnant Holstein × Gyr cows. Different planes of nutrition were established by two feeding regimens: ad libitum or maintenance. Sixty-two nonlactating cows with average body weight of 480 ± 10.1 kg and an age of 5 ± 0.5 years were used. Cows were divided into three groups: pregnant (n = 44), non-pregnant (n = 12), and baseline reference (n = 6). The 56 pregnant and non-pregnant cows were randomly allocated into a feeding regimen: ad libitum or maintenance. To evaluate the effects of days of pregnancy, pregnant and non-pregnant animals were slaughtered at 140, 200, 240, and 270 days of pregnancy. Energy requirements for maintenance differed between pregnant and non-pregnant cows, thus two equations were developed. Net energy and metabolizable energy requirements for maintenance of non-pregnant cows were 82 kcal/kg empty body weight 0.75 /day and 132 kcal/kg empty body weight 0.75 /day, respectively. The efficiency of use of metabolizable energy for maintenance of non-pregnant cows was 62.4%. Net energy and metabolizable energy for maintenance of pregnant cows were 86 kcal/kg empty body weight 0.75 /day and 137 kcal/kg empty body weight 0.75 /day, respectively. Efficiency of use of metabolizable energy for maintenance of pregnant cows was 62.5%. The efficiency of use of metabolizable energy for gain was 41.9%. The efficiency of use of metabolizable energy for pregnancy was 14.1%. Furthermore, net energy requirement for pregnancy was different from zero from day 70 of pregnancy onwards. In conclusion, net energy and metabolizable energy requirements for maintenance of non-pregnant cows are different from pregnant cows. Furthermore, we believe that the proposed non-linear equations to estimate net energy requirements for pregnancy are more adequate than current NRC equation, and should be recommended for Holstein × Gyr cows.