An “Amino acid (AA) partial deletion method” was used in this experiment to study the limiting sequences and appropriate ratio of lysine (Lys), methionine (Met), and threonine (Thr) in the diets of 7- to 9-month-old Holstein heifers. The experiment was conducted for three months with 72 Holstein heifers (age = 22 ± 0.5 weeks old; BW = 200 ± 9.0 kg; mean ± standard deviation). Following an initial two weeks adaptation period, heifers were allocated to one of four treatments: a theoretically balanced amino acid diet (positive control [PC]; 1.00% Lys, 0.33% Met, and 0.72% Thr), a 30% Lys deleted diet (partially deleted Lys [PD–Lys]; 0.66% Lys, 0.33% Met, and 0.72% Thr), a 30% Met deleted diet (partially deleted Met, [PD–Met]; 1.00% Lys, 0.22% Met, and 0.72% Thr), and a 30% Thr deleted diet (partially deleted Thr [PD–Thr]; 1.00% Lys, 0.33% Met, and 0.45% Thr). Experimental animals were fed a corn–soybean meal-based concentrate and alfalfa hay. In addition, the animals were provided with supplemental Lys, Met, and Thr (ruminal bypass). The results found no differences in the growth performance and nitrogen retention between PD–Thr treatment and PC treatment (p > 0.05). The average daily gain (p = 0.0013) and feed conversion efficiency (p = 0.0057) of eight- to ninr-month-old heifers were lower in both PD–Lys and PD–Met treatment than those in PC treatment. According to growth performance, Lys was the first limiting AA, followed by Met and Thr. Moreover, nine-month-old Holstein heifers in PD–Lys treatment and PD–Met treatment had higher levels of serum urea nitrogen (p = 0.0021), urea nitrogen (p = 0.0011) and total excreted N (p = 0.0324) than those in PC treatment, which showed that nitrogen retention significantly decreased (p = 0.0048) as dietary Lys and Met levels decreased. The limiting sequence based on nitrogen retention was the same as that based on growth performance. The appropriate ratio of Lys, Met, and Thr in the diet based on nitrogen retention was 100:32:57. In summary, the limiting sequence and appropriate amino acid ratio of Lys, Met, and Thr for seven- to nine-month-old Holstein heifers fed a corn–soybean meal-based diet were Lys > Met > Thr and 100:32:57, respectively.

This study was conducted to investigate the effect of three rates of prepartum dietary concentrate feeding on the milk performance, energy balance, and rumen fermentation of Montbéliarde–Holstein crossbred cows. Eighteen transition Montbéliarde–Holstein crossbred cows with similar days of gestation (258 ± 12 day) and body weights (622 ± 44 kg) were selected and randomly divided into three groups. In the prepartum period, the addition of concentrates accounted for 0.3% (low concentrate, LC), 0.6% (medium concentrate, MC), and 0.9% (high concentrate, HC) of the cow’s body weight. The forage was corn stover, which was fed to the cows ad libitum with free access to water. Postpartum, all of the cows were fed a common lactation total mixed ration. The experimental period lasted from 21 days prepartum to 28 days postpartum. The energy balance (EB), net energy intake (NEI), and dry matter intake (DMI) of the HC group were greater than those of the other groups (p < 0.05). Likewise, the non-esterified fatty acids (NEFA), β-hydroxybutyric acid (BHBA), and total bilirubin (TBIL) in the blood of the LC group had significantly higher concentrations than they did in the other groups (p < 0.05). Moreover, the increase in the level of dietary concentrate had no significant effect on the rumen fermentation parameters (p > 0.05), and the total intestinal digestibility of dry matter (DM), crude protein (CP), and ether extract (EE) in the HC group was significantly higher (p < 0.05) than it was in the other groups during the prepartum period. In conclusion, the administration of the MC diet in the prepartum period had no negative effect on the performance and rumen fermentation of postpartum dairy cows and can satisfy the energy needs of prepartum dairy cows. Therefore, under our experimental conditions, the 0.6% prenatal concentrate feeding amount was the most appropriate for Montbéliarde–Holstein crossbred cows.