الفهرس 
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Abstract
The purpose of this study was to look into the association between some risk factors and subfertility in Holstein cows raised under the Egyptian subtropical weather. Performance records from 2040 cows calving between years 2016 and 2017 with no repetition per cow were used. Following data processing, the maximum number of lactations used in descriptive statistics and hypothesis testing was 1832 (89.8 percent). Pregnancy by 120 DIM (PREG120), repeat breeder (RB) cows, number of services per cow, Days in Milk at First Observed Estrus (DIMFH), Days in Milk at First Breeding (DIMFB), Pregnancy by 400 Days in Milk and Days Open were the reproductive variables studied.
The following results have been obtained:
• The mean intervals from calving to first observed estrus, and to first AI were 43.7 and 67.8 days, respectively. On average, cows required 4.3 services and 173 DIM (median 149 d) to conceive. Approximately half (50.5%) of the cows received their first insemination between 60 and 80 DIM, most (87.9%) of them had a first AI between 50 and 90 DIM, and practically all cows (99.1%) were bred by 130 DIM.
• About 13.5%, 17.5% and 21.2% of cows became pregnant by 85, 100 and 120 DIM, respectively. Moreover, only 10% of cows became pregnant to first AI. Cumulative conception rate after a second through a fifth AI was 21.9%, 32.5%, 40.5% and 46.3%, respectively.
• High-yielding cows, on the other hand, were 49 percent less likely to be PREG120 than low-yielding cows and the mean proportion of PREG120 in low-producing cows was 9 percent higher (P<0.05).
• In terms of calving season, spring (OR: 0.58, P = 0.002) and summer (OR: 0.50, P = 0.006) calvings had lower odds of PREG120. Furthermore, cows calving in the spring and summer months were PREG120 in lower proportions (P<0.05) than cows calving in the winter and fall months.
• Inseminating cows for the first time after 65 DIM was negatively associated with the odds of PREG120 (OR: 0.60, P<0.001), and the proportion of cows becoming PREG120 was 7% less (P<0.01) than that when first AI occurred at earlier DIM.
• The estimated odds of PREG120 decreased by 38 percent (P = 0.007), 68 percent (P 0.<001), and 36 percent (P<0.01), respectively, for cows with lameness, mastitis, and reproductive disorders. The corresponding proportion of PREG120 cows was 6, 15, and 6 percentage points lower as compared to non-affected cows.
• When compared to low-producing, winter-calving, and non-affected cows, moderate and high milk yield animals in the current lactation, summer calving season, and affliction with lameness, mastitis, or reproductive disorders were all linked to an elevated risk of RB.
• Cows that began lactations in the fall months were 50% less likely to be RB, whereas those who calved in the summer months were 2.18 (P<0.001) times more likely to be RB than those who calved in the winter months. Moderate and high milk producers were 1.59 (P = 0.027) and 2.08 (P = 0.002) times more likely to be POOR cows than low yielding Holsteins. Furthermore, a higher number of high-yielding cows (89 percent vs. 79 %, P<0.05) were rated as POOR than low-yielding cows.
• The cow had a higher risk of being POOR whether she calved in the spring (OR: 1.75, P = 0.002) or summer (OR: 1.98, P = 0.007) when compared to lactations started in the winter months. In addition, the proportion of POOR cows in spring and summer calvings was greater (0.88 and 0.89, respectively) than in winter (0.80) and fall (0.82) calvings.
• Cows who had their first insemination after 65 DIM had a 67 percent higher chance of being classed as POOR, with 7% of them being categorized as POOR. Prior to confirmed pregnancy, cows with lameness, mastitis, or a reproductive problem had a 1.73, 3.04, and 1.63 times increased (P<0.01) likelihood of becoming POOR, respectively. When compared to non-affected cows, the proportion of POOR cows was 7, 15, and 6 percentage points greater (P<0.01) for the three diseases, respectively.
• Cows in the moderate- and high-milk groups needed 0.77 and 1.65 (P<0.01) more AI for pregnancy, respectively, than cows in the low-producer group. <Cows who calved in the winter, spring, and summer months required 0.48 (P<0.05), 0.60 (P<0.01), and 1.22 (P<0.01) more AI, respectively, than cows that calved in the fall. Lame cows also had higher NSC (+0.44, P<0.01) and mastitis (+1.05, P<0.01) than unaffected cows.
• The interval between calving and the first detected heat (DIMFH) was 43.7 days up to 200 DIM. Only 25% of cows were initially observed in estrus after 56 days.
• Cows in their first lactations experienced their initial estrus 4.6 and 4.4 days later (P<0.05) than cows in their second and third lactations, respectively.
• When compared to non-affected cows, cows with lameness, clinical mastitis, or reproductive disorders had their first heat 4 (P<0.05), 6.8 (P<0.01), or 2.9 (P<0.05) days later after calving. DIMFB, on the other hand, was unaffected by milk production levels or calving season.
• The day after calving at first insemination was 5 days (P<0.01) earlier in cows in their second or higher lactations compared to first parity. Moderate and high yielding had significantly longer intervals (LSM ± SE: 70.1 ± 0.77 and 70.6 ± 0.92 d, P<0.01) to first breeding relative to cows with the least milk production (65.1 ± 1.4 d).
• Cows who had never been seen lame previous to pregnancy had a 3.4-day (P<0.01) shorter interval to first breeding than lame cows. Clinical mastitis significantly (P<0.01) prolonged DIMFB by 4.6 d. DIMFB, on the other hand, was unaffected by calving season or affection with a reproductive illness.
• In 25% of the cows, the calving conception interval (CCI) was 91 days or less. Furthermore, the DO of all cows up to 400 DIM averaged 184 days (median 167 days), with 25% of cows open for 238 days or more. More than 75% and 44% of all cows are still non-pregnant after 120 and 200 DIM, respectively. Cows in the moderate and high milk groups had a lower hazard (0.77 and 0.67) for PREG400 and had 21 (P<0.05) and 31 (P<0.01) days longer DO when compared to low-yielding cows.
• Spring calving was associated with a lower chance of PREG400 than winter calvings, despite having a shorter DO (180 days) than winter (215 days) and summer calvings (241 d). Cows inseminated after 65 days in the postpartum period were 22% less likely to become PREG400 and had 26 days (P<0.01) more DO than cows inseminated earlier (65 DIM).
• PREG400 had a negative relationship with lameness, clinical mastitis, and reproductive problems, and all significantly (P<0.01) extended the DO. The corresponding HR was 28%, 44%, and 26% lower, while the open period was 24, 49, and 36 days longer, respectively, than in non-affected counterparts.