The objective was to determine relationships among concentrations of insulin-like growth factor-I in serum, energy balance, body condition, and ovarian activity during early lactation. From 0 to 12 wk postpartum, 11 pluriparous Holstein cows were individually fed a total mixed diet and bled twice weekly for quantification of insulin-like growth factor-I and progesterone. Estrous behavior was monitored twice daily and body condition scores were recorded weekly. Individual feed intake and milk production were recorded daily and milk composition and BW were measured weekly. Cows with positive (3.43 Mcal/d; n = 5) energy balance during the first 12 wk postpartum had greater concentrations of insulin-like growth factor-I in serum and greater luteal-phase progesterone secretion than in cows with negative (-1.69 Mcal/d; n = 6) energy balance. Interval to first ovulation or first estrus did not differ between cows with positive versus negative energy balance. Correlation coefficients among weekly averages revealed positive correlations between energy balance and serum progesterone, and energy balance and serum insulin-like growth factor-I. Body condition scores were not correlated with energy balance or serum insulin-like growth factor-I. We conclude that reduced luteal activity that accompanies negative energy balance may be associated with reduced concentrations of insulin-like growth factor-I in serum.

Ten Holstein cows averaging 120 d in lactation were arranged in replicated 5 x 5 Latin squares with 3-wk periods to evaluate the role of sulfur (S) in the dietary cation-anion balance equation. Diets were based on corn silage in Exp. 1 and sorghum silage in Exp. 2. Supplemental S and chloride (Cl) from the double sulfate of potassium and magnesium and CaCl2 were used to manipulate dietary cation-anion balance from 0 to +30 meq when expressed as meq [(Na + K)-(Cl + S)]/100 g diet DM and from +19 to +49 meq when expressed as meq [(Na + K)-Cl]/100 g diet DM. Blood pH was not affected by cation-anion balance, although both S and Cl supplementation tended to lower pH. Blood HCO3- and urine pH decreased and plasma calcium (Ca) and urinary Ca excretion increased as anion was added to the diet. Milk fat production tended to be increased by the low S supplementation. Dietary Cl and S had similar effects on acid-base status. Therefore, we suggest that S be included with Cl in the dietary cation-anion balance equation for lactating dairy cows as follows: meq [(Na + K)-(Cl + S)]/100 g diet DM. Although response of acid-base status to S and Cl was similar, as more data comparing the acidogenicity of S vs Cl become available, it may be necessary to include a modifying coefficient for S in the equation to adjust for differences between S and Cl in acid-generating potential. This coefficient may be further dependent on the dietary source of S.

Our objective was to evaluate the effectiveness of a low dietary cation-anion balance (DCAB) in preventing milk fever and udder edema in dry cows consuming a high-Ca diet and to evaluate the effect of this diet on calves delivered by these cows. Seventy primiparous or multiparous cows and 50 pregnant heifers were offered alfalfa hay-based diets beginning 4 wk before their projected calving date. Diets contained 1.6% Ca and a DCAB of -3 or +9 mEq/100 g of diet DM. Blood and urine samples were collected weekly from 3 wk prepartum until 3 wk postpartum. Blood samples were collected from calves at parturition and weekly thereafter for 3 wk. Feeding a low vs high DCAB in a high-Ca diet for 3 wk prepartum did not reduce the incidence of milk fever; this lack of response may have been attributable to the relatively low DCAB of each diet and the small difference in DCAB between the two diets. Udder edema seemed to regress more rapidly postpartum for cows that had consumed the low DCAB during the dry period. Test diets fed to prepartum cows did not affect systemic acid-base status or plasma mineral content of their calves, although plasma Ca was somewhat lower for calves from cows consuming a low DCAB and was higher for calves from primigravid cows. Correlations of plasma mineral concentration of the cows with those of their calves were highest for plasma Ca (r = .75; P less than .001). We conclude that the prophylactic effects on the occurrence of milk fever of feeding a low DCAB during the dry period may be absent when diets contain greater than 1.6% Ca and DCAB is greater than or equal to -3. The cation-anion balance of the diet consumed by dry cows did not affect the acid-based status or plasma mineral content of their calves.

The objective was to determine the effects of dietary inert fat on estimated energy balance, hormones in plasma, and reproduction during early lactation. From wk 0 to 12 postpartum, 14 pluriparous Holstein cows were fed individually a TMR, and blood samples were taken twice weekly for quantification of IGF-I, progesterone, and cholesterol. During wk 5 to 12, one-half of the cows remained on the TMR, and the other half were fed the TMR containing inert fat at 1.8% of dietary DM. Estrous behavior was monitored twice daily, and body condition scores were recorded every 4 wk. Cows fed inert fat between wk 5 and 12 postpartum had similar concentrations of IGF-I in plasma but greater luteal phase progesterone secretions than cows fed the control diet. Total cholesterol in plasma also was greater in cows fed inert fat than in cows fed the control diet. Intervals to first, second, and third ovulation or estrus did not differ among cows fed control or inert fat diets. Body condition scores, daily DMI, and milk production were not affected by dietary inert fat. Inert fat fed to cows between wk 5 and 12 postpartum did not affect ovulatory activity but may enhance luteal activity.