Practical relationships were determined between milk production, health, and reproduction with the amount and use of body fat in high producing lactating Holstein dairy cattle. Approximately 350 cows and heifers > 15 mo of age in a high producing herd were assigned body condition scores at monthly intervals for 24 mo. Production of 305-d FCM averaged 9541 kg (range 8826 to 10,818 kg). Body condition score at each of four calvings at 30, 60, 90, 120, and 305 DIM in each parity and loss in score in each lactation were summarized. Multiple regression related scores to milk and milk fat production, reproduction, and disease variables within and among lactations. No difference in score occurred at calving or at dry-off among parities. The range of body condition scores was less than is commonly reported; however, loss of condition increased with increasing parity from .3 in first lactation to .9 body condition score units in lactations > or = 4. The body condition score varied quadratically with DIM but, at a given DIM, was not related to the daily milk production on that DIM. Parity had a stronger relationship with milk and milk fat production than did body condition score. However, within lactation, body condition score at calving and the loss of score were related quadratically to milk production. No significant relationships of body condition score to the incidences of pyometra, metritis, retained placenta, cystic ovarian disease, AI per conception, days to first AI, or dystocia existed in this herd.

The adaptations of fat synthesis in adipose tissue to lactational state, rate of milk production, and dietary fat intake were determined for dairy cows. Lipogenesis and esterification were determined in cows of average or high genetic merit for milk production and fed either a control TMR of corn silage, alfalfa, and concentrate (2.5% fat; 1.47 Mcal of NEL/kg); a TMR with whole cottonseeds replacing 12% of the concentrate (4.4% fat; 1.49 Mcal NEL/kg); or a TMR with 12% cottonseeds and 2.7% of Ca salts of fatty acids (6.0% fat; 1.53 Mcal of NEL/kg). Dietary treatments began on d 17 of lactation and continued for 288 d. Lipogenesis and esterification decreased equally from 15 d prepartum to 15 d postpartum in all groups. Cows of high merit had lower rates of lipogenesis and esterification at d 60 than did low merit cows but had higher rates of lipogenesis at d 120. Rates of lipogenesis were decreased by dietary fat treatments. Esterification rates were lowest on the intermediate fat TMR and highest on the highest fat TMR. Lipogenesis was decreased logarithmically by dietary fat intake; this effect was greater as lactation progressed. Adipocyte size and body fat mass decreased during early lactation and then increased for all treatment groups. Supplemental dietary fat reduces de novo synthesis of fatty acid, and this effect increases as lactation progresses.

The objective of the study was to establish and compare equations that would estimate the body fat content of lactating dairy cows from different indirect techniques. The techniques used were body condition scoring, dilution of D2O in body water, and determination of mean fat cell size diameter of the subcutaneous, abdominal, and perirenal depots. Each technique was validated against direct determination of body fat content of the same lactating cows. To apply equations to high producing, lactating dairy cows, cows were from a herd producing more than 9500 kg of FCM/305 d, were lactating, and were in less than average body condition. Eight days prior to slaughter, a single injection of D2O was injected into the jugular vein, and body dilution was followed for 4 d. Cows were scored for body condition on the day of injection and weighed daily for the 4 d prior to slaughter. Samples of subcutaneous, perirenal, and omental adipose depots were taken, and adipocyte size and number were determined. Body fat was not predicted well by D2O space alone, but inclusion of BW did improve the prediction of body fat from this variable. The best equations were derived from use of BW with body condition score or subcutaneous fat cell diameter: observed body fat = -122.1 + .21 x BW + 36.0 x body condition score, and -195.6 + .290 x BW + .927 x subcutaneous fat cell diameter; standard errors of the estimate were 4.6 and 5.5 kg, respectively. Equations using diameters of abdominal and perirenal fat cells gave similar relationships. Equations using all four predictors (live BW, fat cell diameter, condition score, and D2O space) were only slightly improved over these equations. Thus, use of body condition score, adipocyte diameter, and BW in laboratory and field conditions may help in the study and management of the use of body fat in lactating dairy cows.

Holstein cows were assigned to diets containing no supplemental fat, supplemental fat from whole cottonseed, or supplemental fat from whole cottonseed plus Ca salts of fatty acids (Megalac). The TMR contained 46% forage and 54% concentrate or mixtures of concentrate and whole cottonseed on a DM basis and were fed from wk 3 through 44 of lactation. The mean fat content of the three diets was 3.0, 4.7, and 6.4% of DM for control, whole cottonseed, and whole cottonseed plus Ca salts of fatty acids, respectively. Supplemental fat increased NEL intake, percentage of milk fat, milk fat production, and rate of recovery of BW and body condition. Supplemental fat decreased milk protein production in early lactation, but not in late lactation. Addition of supplemental fat had no significant effect on ruminal concentration of VFA, NH3 N, or in situ digestibility of fiber. The proportion of unsaturated fatty acids in milk fat was increased with supplemental whole cottonseed or whole cottonseed plus Ca salts of fatty acids. During the first 3 mo of lactation, the proportion increased of fatty acids C14 or less, C16, and C18:2. Proportion of fatty acids C16:1 and C18:1 correspondingly decreased. The change in composition of milk fatty acids during early lactation is consistent with the use of body fat for milk synthesis.