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Concentrate Feeding Strategy in Lactating Dairy Cows: Metabolic and Endocrine Changes with Emphasis on Leptin
© The Author(s); licensee BioMed Central Ltd. 2003
Published: 31 March 2003
Relationships between leptin and metabolic, enzymatic, endocrine and zootechnical traits were assessed in 90 multiparous Holstein cows [mean 9'500 kg energy-corrected milk/305 d], held in a research farm from wk 2 ante partum (a.p.) to wk 20 post partum (p.p.). Concentrates (8 MJ NEL/kg DM) were fed by automatic feeders for 24 h at 30% (C30) or 50% (C50) of total dry matter (DM) intake (DMI) from wk 1–10 p.p. and were then continuously lowered to 2.4% and 4% until wk 34, resp. Roughage (6 MJ NEL/kg DM) was fed ad libitum. DMI was measured continuously during 24 h. Milk yield and body weight (BW) were determined twice/d. Milk composition was determined 4 times/wk and milk acetone (AC) was measured weekly. Blood samples for the determination of metabolites, hormones, enzymes and electrolytes were obtained in wk 2 a.p. and weekly from wk 1–16 and in wk 20 p.p. between 0730 and 0900. Body condition scores (BCS) and ultrasonic measurements of backfat thickness, long. dorsi muscle diameter and fat depth in the pelvic area were evaluated a.p. and in wk 1, 4, 8, 12, 16 and 20 p.p. In wk 4 p.p., metabolic and endocrine profiles were studied in 10 cows of C30 and C50, resp., by hourly blood sampling from 0730–1530. Metabolites and enzymes were measured photometrically and hormones were determined by species-specific radioimmunoassays. Results: Roughage intake was higher, but total DMI was considerably lower in C30 than C50. Peak milk production (42.1 and 43.8 kg/d in C30 and C50, resp.) was reached in wk 4 p.p., but mean yields of C30 cows were only 1.28 kg/d lower than of C50 cows. Energy balance (EB) was positive a.p., reached a nadir at wk 2 p.p. (-46.0 and -29.6 MJ NEL in C30 and C50, resp.) and then increased up to wk 20 p.p. Metabolic stress was more marked in C30 than C50 cows, expressed by lower levels of glucose, leptin, insulin, IGF-1, T3, milk protein and lactose, but higher levels of NEFA, BHBA, GH and milk AC, and a faster decrease of BCS and backfat thickness in C30 than C50 cows over the first 20 wk p.p. (P < 0.05). Blood BHBA and milk AC concentrations peaked in wk 4 p.p. Enzyme activities were higher in C30 than C50 cows over the first 8 wk p.p. Concentration of Ca was higher and of Cl lower in C30 than C50 cows. The measure of determination of the linear mixed-effects model to assess relationships between leptin and metabolic, enzymatic, endocrine and zootechnical traits was high (R2 = 0.85). However, for leptin the individual cow accounted for most of the variance (R2 = 0.61). Leptin concentrations were positively associated with BCS, EB, BW, cholesterol, albumin, insulin and IGF-1, and negatively with total DMI and T3, and were higher in cows calving in spring than in fall, i.e. leptin was positively correlated (P < 0.001) with daily photoperiod (r = 0.26), mean daily light intensity (r = 0.33) and mean daily ambient temperature (r = 0.33). In conclusion, leptin is one of several traits which are connected with EB, but it is also related to other factors.
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