Fig. 1

The flowchart of this study. All animals were fed the same diet, kept under the same conditions, and housed together from birth (Table S9). During the preweaning phase, all kids were fed milk, alfalfa hay and concentrate mixture, and the weaned animals (3 months old to ~ 13 months old) were fed total mixed ration (TMR) with a forage to concentrate ratio of 60:40. After delivery, goats were fed TMR with forage:concentrate rations of 50:50. ^1,2 From 99 young goats enrolled in this study, 15 goats with the highest average daily gain (ADG) were selected as the HADG group (ADG: 132.5 ± 1.5 g/day); 15 goats with the lowest ADG were selected as the LADG group (ADG: 88.2 ± 1.2 g/day). ^3,4 After delivery of their newborn offspring kids, 84 of 99 healthy lactating goats remained, and 15 goats were excluded. In the HAL group, 13 lactating goats of 15 HADG goats remained and were renamed the HAL group; in the LAL group, 12 lactating goats of 15 LADG goats remained and were renamed the LAL group. ^5,6 Among these 84 lactating goats, 15 lactating goats with the highest milk yield were selected as the HMP group (average daily milk yield: 2.82 ± 0.04 kg/day), and 15 lactating goats with the lowest milk yield were selected as the LMP group (average daily milk yield: 1.51 ± 0.03 kg/day), according to the milk yield recorded every 7 days over the first whole lactation period ADG: average daily gain, AA: amino acid, HADG: young goats with high average daily gain, LADG: young goats with low average daily gain, HAL: lactating goats of HADG, LAL: lactating goats of LADG, HMP: lactating goats with high milk yield, LMP: lactating goats with low-milk yield