During the conduct of an experiment designed to examine the nutritional management of dairy cows in late pregnancy, four cows out of 72 suffered from acute haemoglobinuria two to four weeks after calving. Thirty-six thin and 36 fat cows were individually fed one of three diets based on a total mixed ration with different energy or protein concentrations during the last 3 to 4 weeks before expected calving date. After calving, cows grazed pasture and were offered 6 kg dry matter of pelleted concentrates daily. The P concentrations of the feeds offered suggested that the cows' diets were marginally deficient in P relative to requirements. Plasma P concentrations were significantly (P < 0.05) lower in fat cows than in thin cows during the first 6 weeks of lactation (0.87 versus 1.12 mmol/L), but precalving diet had no effect (P > 0.05). Concentrations of plasma inorganic P of the four fat cows that developed acute haemoglobinuria were less than 0.3 mmol/L. However, plasma P concentrations in another 12 cows, none of which displayed overt symptoms, declined to similar levels. It appeared that inadequate dietary P may have predisposed cows to acute haemoglobinuria, but the precipitating cause was not readily obvious.
Insulin-like growth factor-1 (IGF-1) is associated with the reproductive performance of the dairy cow. The association between IGF-1 concentrations in early lactation and interval to first oestrus and conception are widely reported (1). Changes in plasma IGF-1 in mid and late lactation, which may also be associated with advancing pregnancy, have not been reported in the dairy cow. Given the relationship between bovine somatotropin and IGF-1 (2), it would be expected that plasma IGF-1 concentrations would increase as the pregnancy proceeds. The aim of this study is to determine if pregnancy would alter the pattern of changes in plasma IGF-1 concentrations in mid and late lactation. The study was conducted at the Department of Primary Industries, Kyabram, Victoria. All cows were high-producing multiparous Holstein-Friesians, receiving a pasture-based diet. Plasma samples were collected frequently throughout lactation and analysed using the DSL non-extraction IGF-1 ELISA kit. Data were analysed using univariate analysis of variance, with body condition score as a covariate. Data for pregnant cows (n = 24) were analysed relative to actual conception dates for each cow. This was compared to that from non-pregnant cows (n = 10) relative to day 86 of lactation (average conception day of pregnant cows). Average plasma IGF-1 of both pregnant and non-pregnant cows peaked at 103 ng/mL at around week 12 of lactation. It decreased dramatically over the next 5 weeks to 67 ng/mL, and remained relatively constant over the next 10 weeks. Plasma IGF-1 of pregnant cows was numerically higher than that of non-pregnant cows throughout the data collection period. This difference increased after conception and became statistically significant 15 weeks post-conception (P<0.05). At that time, plasma IGF-1 concentrations were 75 ng/mL for pregnant cows and 53 ng/mL for non-pregnant cows. This difference is expected to increase as the pregnancy proceeds.
Low plasma concentrations of IGF-I in early lactation have been associated with extended periods of calving to first ovulation in dairy cows (1). The objectives of this study were to compare plasma concentrations of IGF-I in cycling and anoestrous Holstein-Friesian (HF) cows and to establish any relationship between these concentrations and intervals from calving to first ovulation. Experiments 1 and 2 were conducted in 2001 and 2002. Before the AI program commenced in 2001, 23 of the 72 cows had >1 oestrous cycle, 26 had only 1 cycle, 10 cows ovulated but did not display signs of oestrus and 13 cows remained anovulatory. Year 2 included 30 cows from Year 1 that cycled early (12), late (12) or very late (6). Plasma concentrations of IGF-I were measured at calving, and at 1, 5 and 10 weeks into lactation with an ELISA. Experiment 3 involved 40 cycling and 30 anoestrus HF cows. Plasma concentrations of IGF-I were measured on Days 0 (day of insemination), 6, 12 and 18. In Experiment 1, cycling cows had higher (P<0.01). mean plasma concentrations of IGF-I than anoestrous cows; concentrations ranged from 48.8 ± 5.9 to 68.5 ± 4.4ng/mL for the anoestrous and cycling cows respectively. Cows that were anovulatory had a longer interval from calving to first ovulation than the other three groups (76.5 ± 2.5 v. 39.9 ± 2.9 days, P<0.001). Early cycling cows in Experiment 2, had higher plasma concentrations of IGF-I compared to the very late cycling cows (96.5 ± 10.9 v. 51.4 ± 15.4 ng/mL, P<0.05). In Experiment 3, plasma concentrations of IGF-I in cycling cows were higher compared to anoestrous cows (76.50 ± 3.85 v. 60.30 ± 4.4ng/mL, P<0.01). Cows with low IGF-I concentrations in early lactation are at greater risk of experiencing extended intervals from calving to first ovulation and of not showing signs of oestrus at that ovulation.
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