Given the recent increases in feed cost, the demand for rice straw has been increasing on dairy farms because it is cheaper than expensive imported forages. Therefore, it is necessary to study the effect of rice straw feeding on the growth and productivity of dairy heifers. This study compared how feeding tall fescue and rice straw affects the growth, age at first calving, and feed cost of heifers. we compared the growth, age at first calving, and feed cost for each group during the breeding period. Body height was higher in the tall fescue-fed group than in the rice straw-fed group (p<0.05). The length of the growing stage was significantly shorter in the tall fescue group than in the rice straw group (p<0.001) and the age at calving also showed a significant reduction in the tall fescue group compared to the rice straw group (p<0.001). However, the feed cost was lower in the rice straw group because of the difference in the unit price of forage (p<0.001). Based on these results, during the growing period, the rice straw group had delays in growth and the age at first calving compared to the tall fescue group, but also had reduced feed costs in the short term.

Growth rate during rearing, which varies depending on provided nutrition, has been related with age at 1st calving (AFC). This study investigated the effect of upgrowth parameters during the rearing period on the reproduction of nulliparous Holstein heifers. The study comprised 77 successively born heifers from the same herd. Growth rate and fertility traits were measured during rearing and fertility parameters were recorded in lactations 1. Growth parameters (body weight, height, heart girth and body length) were measured at the approximate birth time, 270 and 450 d of age. Reproduction data collected included age at 1st breeding, number of services per conception (S/C), pregnancy rate to 1st artificial insemination, AFC. Animals were subsequently divided into 4 AFC groups for analysis: <23 mo, 23∼ 25 mo, 26∼30 mo and >30 mo. The AFC reflected both upgrowth rate and heifer reproduction, with later calving heifers smaller. Increased skeletal growth (at 270 and 450 d) was related with a reduced AFC (p<0.05). Early calving animals (<23 mo) had the best reproduction as nulliparous heifers, with most conceiving at first service (87.5%). Fertility in the first lactation was the worst in the oldest AFC group (>30 mo). In the 1st lactation period, a number of services per conception (3.1±0.3) increased with increasing AFC (>30 mo). Sub-optimal upgrowth related with an increased AFC could be mitigated by improved monitoring of replacement heifers during the rearing period.

Raising replacement heifers is important aspect of dairy farm management that can be characterized as a long-term performance and high-cost production period. This study was investigated the effect of month of age at the first pregnancy on calving difficulty of Holstein heifers. Heifers was inseminated with semen of easy-calving sire and the reproductive performance was compared for the effect of first pregnancy at 12-14 months of age (12 month old), 15-16 months of age (15 month old), 17-19 months of age (17 month old) and > 20 months of age (20 month old) in Holstein heifers. Holstein heifers showed different easy calving score (ECS) depending on their ages; frequency of ECS 1 was 55.2%, 64.9%, 59.4% and 52.0% at 12, 15, 17 and 20 month of age, respectively. Frequency of ECS 4 was 5.2%, 1.8%, 6.3% and 4.8% at 12, 15, 17 and 20 month of age, respectively. The rates of retained placenta postparturition in first pregnancy age category was 12.3% at 12 months of age, 5.3% at 15 months of age, 9.4% at 17 months of age and 19.0% at 20 months of age. When It was evaluated by present results, the reproductive performance like easy calving score (ECS), retained placenta rates, and abortion and stillbirth rates of heifers which was inseminated at 14 months old or less and at 17 months old or more was reduced. Therefore, the first pregnancy age for optimum reproductive performance was 15-16 months.