Effect of supplemental beta-carotene on incidence and responsiveness of ovarian cysts to hormone treatment

Sixty-two multiparous and 35 primiparous Holstein cows were assigned randomly at 10 days postpartum to receive a ration with or without 300 mg beta-carotene/cow per day. Multiparous and primiparous cows were grouped separately and group-fed complete rations once daily. Incidence of ovarian cysts (26% by rectal palpation) was not affected by beta-carotene fed. Multiparous cows had greater incidence (39%) of ovarian cysts than primiparous cows (11%). Fifty-seven percent of cysts were classified follicular by rectal palpation. Progesterone concentration of milk also was used for diagnosis of type of cyst. Cows with ovarian cysts and with progesterone concentrations in milk less than 1 ng/ml were classified follicular, and those having concentration greater than 1 ng/ml were classified luteal. As determined by milk progesterone, rectal palpation was more accurate for diagnosis of luteal cysts than for diagnosis of follicular cysts. Progesterone concentrations of milk for animals with luteal and follicular cysts were 10.66 +/- 1.29 and .37 +/- .07 ng/ml. beta-Carotene did not affect response or days to respond to treatment with human chorionic gonadotropin or gonadotropin-releasing hormone. Supplemental beta-carotene was not beneficial for reducing incidence of ovarian cysts in cows receiving an adequate supply of beta-carotene in their diet.     

Milk progesterone in postpartum and pregnant cows as a monitor of reproductive status.

Milk samples were analyzed for progesterone content by a petroleum ehter extraction and competitive protein binding assay validated for milk. In one experiment, 11 cows were sampled twice daily for 24 days beginning with an observed estrus 15 to 45 days postpartum, and again 19, 21, 23, and 25 days after breeding. Progesterone values during the estrous cycle paralleled those for blood plasma but were slightly higher at estrus (1.49 ng/ml milk) and maximum (9 ng/ml) on days 11 to 16 of the estrous cycle. After breeding, cows later diagnosed pregnant averaged 7.12 ng/ml while those later found to be nonpregnant averaged 2.36 ng/ml. All diagnoses of pregnancy were correct. In a separate experiment there was no difference between milk from front and rear quarters, but progesterone was highest in last milk, intermediate in composite milk, and lowest in first milk.     

Detection of estrus in dairy cows by electrical measurements of vaginal mucus and by milk progesterone.

Electrical resistance (ohms) of mucus were analyzed in 20 postpartum Holstein cows by use of a probe inserted into the anterior vagina every other day for 30 days. Composite milk samples were taken on the same day, and progesterone was determined by radioimmunoassay. Cows were observed twice daily for standing estrus and reproductive organs palpated weekly per rectum (rectal palpation). Fifteen cows which were cycling showed increasing progesterone 6 to 7 days after the onset of estrus with values of 8.1 to 10.0 ng progesterone/ml milk on days 10 to 17. Concentrations had declined rapidly 2 days before onset of the next estrus. Progesterone in milk was affected by cow and by day of the cycle. Electrical resistance followed a similar cyclical pattern, but variability was large and only cows differed. The correlation between milk progesterone and mucus resistance was .22. Progesterone concentrations for four cows with follicular cysts fluctuated randomly with a mean of 2.6 ng/ml. Mean resistance of vaginal mucus was 44 omega for both cycling and cystic cows, indicating that a single measurement of electrical resistance every 2nd day was unreliable in distinguishing physiological states. One cow had high progesterone in milk on days 19 to 25 and was diagnosed pregnant by rectal palpation 3 wk later. Cows were not seen in estrus 28% of the time when milk progesterone and rectal palpation indicated they were in the follicular phase of the estrous cycle and were cycling.     

Blood and milk progesterone in pregnant and nonpregnant buffalo

Changes in progesterone concentration of blood and milk were measured by radioimmunoassay in 10 Murrah buffalo up to 40 days after insemination. Progesterone concentration in blood plasma at estrus was .1 ng/ml which rose to a peak of 3.6 ng/ml on day 13. It continued to increase in animals that conceived but dropped to .6 ng/ml on 3 days before next estrus in those that failed to conceive. The average concentration of progesterone in milk was .5 ng/ml at estrus; it increased to 18 ng/ml on day 15, and thereafter it declined to 4.4 ng/ml 3 days preceding next estrus in nonpregnant animals. In pregnant animals, it was maintained and elevated further to 24.8 ng/ml on day 37. Progesterone in milk was four to five times higher than in blood plasma.     

Relationship of the estrous cycle to milk composition.

The relationship of the estrous cycle to milk composition was examined in 15 Holstein cows in first lactation which were approximately 45 days postpartum. Composite milk samples were collected twice daily and analyzed for progesterone, fat, protein, total solids, sodium, potassium, magnesium, calcium, and somatic cells. Milk progesterone was minimal (less than ng/ml) from day -1 to day 2 (day 0 = estrus) of the estrous cycle and then increased at a relatively constant rate through day 15. Milk yield and sodium and magnesium concentrations of the milk varied with days of the estrous cycle. Mean milk yield was highest and sodium and magnesium concentrations were lowest on day 1. However, sodium concentration of the milk was the only component that varied significantly during the 3 days centered on estrus (days -1, 0, and 1). No other milk component changed significantly during the estrous cycle. Although milk yield and composition varied during the estrous cycle, none of these components appeared to be a practical indicator of estrus.     

Induction of Lactation by Two Techniques: Success Rate,Milk Composition,Estrogen and Progesterone in Serum and Milk,and Ovarian Effects

Induction of lactation was attempted in 12 heifers and 12 cows with estradiol benzoate (.011 mg/kg body weight per day) subcutaneous for 10 days or that plus progesterone (.1 mg + .25 mg/kg body weight per day) for 7 days. Milking commenced on day 20 for those treated with the mixture and on day 11 for the others. Lactations were induced (minimum of 4.5 kg of milk/day) in five of six heifers and two of six cows by the mixture and in six of six heifers and three of six cows for estradiol benzoate. Milk production was 44% of herdmates in the 16 induced lactations. Cows on the single treatment had lower production than the other three groups. Ovarian status, cycling, cystic, or static, was affected adversely in 5 of 16 animals induced successfully. Two of the 16, both heifers, carried calves to term following induction. The transition to normal composition of milk was slower for single than double treatment. Lactose increased slowly to normal over the 1st wk of milking while protein decreased slowly. Estrogen and progesterone in milk of induced cows were approximately twice as concentrated as in normal post-parturient cows, probably because milk production was halved.     

Comparison of total and free cortisol in bovine serum and milk or colostrum

Total (free plus protein-bound) and free cortisol concentrations in paired samples of serum and skim milk or colostrum were determined by specific radioimmunoassay after extraction or ultrafiltration. For 11 cows in established lactation mean total cortisol concentrations +/- SE in serum and milk were 4.5 +/- .7 ng/ml and .35 +/- .06 ng/ml, respectively. Concentrations of free cortisol in serum and milk were about .3 ng/ml, which is at the lower limit of the present assay. Following 200 IU Synacthen injection to 5 cows, total cortisol in serum and milk rose to 67 +/- 6.0 ng/ml and 11.4 +/- 1.5 ng/ml by 8 h postinjection, while free concentrations increased to 4.3 +/- .7 ng/ml and 6.5 +/- .8 ng/ml in serum and milk, respectively. Eight additional cows were sampled at 1 to 2 d after parturition, and total cortisol in serum and colostrum was 16.6 +/- 1.6 ng/ml and 4.4 +/- 1.3 ng/ml, and free cortisol was 2.4 +/- .4 ng/ml and 1.8 +/- .5 ng/ml, respectively. Free cortisol concentrations in colostrum or in milk from cows in established lactation, before or after adrenal stimulation, are directly related to free cortisol concentrations in the blood, while the bound cortisol in milk is more related to these two stages of lactation rather than the bound hormone in the blood. Measurement of free cortisol in milk should allow the monitoring of changes in plasma free cortisol in studies of stress in dairy cows.     

Lactational changes in oxytocin release, intramammary pressure and milking characteristics in dairy cows.

Two experiments were conducted to investigate possible changes of milking-related oxytocin release (Expt 1) and of intramammary pressure and milking characteristics (Expt 2) throughout entire lactations in German Braunvieh dairy cows. Mean oxytocin concentrations after stimulation at onset of milking increased from 18.3 +/- 15.9 to 30.7 +/- 24.1 pg/ml in Expt 1 and decreased from 23.9 +/- 17.6 to 15.4 +/- 9.1 pg/ml in Expt 2, respectively, but remained above the level necessary to elicit complete milk ejection in both trials. Premilking baseline intramammary pressure had its maximum in early lactation until about month 4 and then decreased to approximately 50% of its initial level. Ejection pressure followed a similar pattern, but dropped only to approximately 75% of its maximum. This was due to the constant elevation of pressure increase, reaching its highest level in late lactation. Time from commencement of stimulation until maximum pressure exceeded 1 min in almost all instances even in early lactation and increased throughout lactation. Despite the normal decrease of milk yield average milk flow fell only slightly while maximum flow rate remained almost constant. Pressure increase, milk yield and milk flow were not different after 1 min and after extended stimulation. Thus there were no indications of a decreasing sensitivity of the milk ejection reflex during lactation, and milking characteristics were positively affected by intense teat stimulation. Suggestions for practical dairying are made.     

Use of monoclonal antibodies for radioimmunoassay of water buffalo milk progesterone

In order to standardize a radioimmunoassay of milk progesterone as a routine method for confirmation of oestrus and diagnosis of pregnancy in water buffalo, monoclonal antibodies against progesterone were produced. Hybridomas were prepared by fusing spleen cells from a Balb/c mouse immunized with progesterone 11 alpha-hemisuccinate-bovine serum albumin conjugate with the mouse myeloma cell line NS-1. Thirty wells out of 94 secreted anti-progesterone antibodies. Of the ten independent hybridomas derived, one (AF65) was suitable for the quantification of milk progesterone by radioimmunoassay. The tracer used in the assay was progesterone-11 alpha-hemisuccinate [( 2-125I]iodohistamine). The sensitivity of the assay was 50 pg/tube. The mean progesterone concentration at oestrus was 0.8 +/- 0.2 ng/ml increasing to 8.5 +/- 0.8 ng/ml 24 d later in pregnant animals.     

Adrenal responsiveness in pre- and postpartum dairy cows.

Adrenal responsiveness was evaluated by injecting 10 multiparous dairy cows with 200 IU adrenocorticotropin between -13 and -2 days prepartum (I) and postpartum between 24 and 40 h (II) and 21 and 24 days (III). Concentrations of glucocorticoids following injection were influenced by day of injection, temperature, and minimum percent relative humidity but not by breed, breed X injection day interaction, or age of cow. Likewise differences in regressions for adrenal response and mean response (ng/ml) for the three injections were nil. Mean concentrations at peak (45, 60, and 120 min postinjection samples) adjusted for preinjection concentrations also did not differ for the three periods of injection. Mean concentrations of glucocorticoids in plasma for daily samples between -13 and -2 days prepartum were 5.3 +/- .4 (n = 61), reached a peak of 14.8 +/- .3 ng/ml the day of calving, and remained high for 2 days postpartum. Estradiol increased through prepartum sampling from 23.3 to 339.6 +/- 94.1 pg/ml the day of calving, then declined abruptly. Progestins began to decline about -5 days prepartum from mean concentration of 4.09 +/- .62 (n = 25) and attained low concentrations (.30 +/- .06 ng/ml) 2 days postpartum. Although there was a surge of glucocorticoids at parturition, this was not associated with a modification in adrenal responsiveness or with prepartum concentrations of other steroid hormones of plasma. Adrenal potential in prepartum and postpartum dairy cows appears well maintained.     

Effects of pregnancy on pulsatile secretion of LH and gonadotrophin-releasing hormone-induced LH release in sheep: a longitudinal study

Pulsatile LH secretion and its control throughout pregnancy have not been fully determined in sheep. Expt 1 determined the patterns of LH secretion in five ewes on days 10, 20, 60 and 120 of pregnancy and on day 10 postpartum, compared with those on day 10 of the oestrous cycle. Mean (+/- SEM) concentrations of LH declined steadily throughout pregnancy (ANOVA, P < 0.01) and were lower (P < 0.01) on day 60 (0.19 +/- 0.3 ng ml(-1)) and on day 120 (0.18 +/- 0.4 ng ml(-1)) of pregnancy than on day 10 of the oestrous cycle (0.55 +/- 0.04 ng ml(-1)). This decrease was due to a significant reduction in the number and the amplitude of LH pulses. Only on day 120 of pregnancy were progesterone concentrations higher (P < 0.01) than on day 10 of the oestrous cycle. Although concentrations of progesterone on day 10 postpartum were barely detectable, mean LH concentration (0.45 +/- 0.09 ng ml(-1)) was not different from that on day 10 of the oestrous cycle. Expt 2 examined the LH responses in a separate group of four ewes to a physiological dose of GnRH (0.2 microg) on days 10, 20, 60 and 120 of pregnancy and on day 10 postpartum, compared with those on day 10 of the oestrous cycle. The area under the LH response curve and the maximum LH concentrations induced by GnRH declined steadily throughout pregnancy (ANOVA, P < 0.01) and were lower (P < 0.01) on days 60 and 120 of pregnancy than on day 10 of the oestrous cycle, but these parameters were not different between day 10 postpartum and day 10 of the oestrous cycle. Expt 3 examined the LH responses in a separate group of four ewes to a potent GnRH agonist, buserelin (0.5 microg), on days 10, 60 and 120 of pregnancy. The area under the LH response curve and the maximum LH concentrations induced by GnRH were lower (P < 0.01) on days 60 and 120 than on day 10 of pregnancy, but were not different between days 60 and 120. This longitudinal study demonstrates that the pulsatile LH release and pituitary responsiveness to GnRH decreases progressively as pregnancy advances, but does not support the hypothesis that high concentrations of progesterone are solely responsible for the inhibition of pulsatile LH secretion and GnRH-induced LH release during pregnancy in sheep.     

Induction of lactation: lactational, physiological, and hormonal responses in the bovine

Milk yields, physiological responses, and concentrations of plasma hormones were evaluated in 24 attempts to induce lactation in nonlactating dairy cows. Subcutaneous injections of estradiol-17beta and progesterone (.10 and .25 mg/kg body weight per day) for 7 consecutive days were used. Dexamethasone injections (.028 mg/kg body weight per day) on days 18 to 20 were given during 12 attempts at induction. Milking was initiated on day 21. All cows showed proestrus activity within 2 days after the first steroid injection; this subsided, then reappeared in many animals between days 16 to 20. In 14 of 24 attempts mean daily milk production was greater than 5 kg. Actual or projected 305-day lactation milk yields were between 1859 and 5354 kg. However, milk yields of seven induced cows averaged only 73% (32% to 136% range) of their previous natural lactations. Dexamethasone injections increased the number of cows that produced more than 5 kg/day; however, milk yields were not improved. Concentrations of estradiol, estrone, and progesterone in plasma were unaffected by dexamethasone, but concentrations of glucocorticoids in plasma were depressed on days 19 to 22. Concentrations of prolactin (peak and mean) in plasma for six cows each that produced greater or less than 5 kg/day did not differ. However, concentrations of prolactin increased in the week following steroid injections (days 8 to 15) only in those cows that produced greater than 5 kg/day but were elevated in all cows during the 3rd wk.     

Long-term effects of sometribove in lactating cows during a fourth consecutive lactation of treatment: insulin and somatotropin responses to glucose infusion.

The effect of sometribove (USAN, methionyl bST) on the endocrine pancreas and blood bST concentrations was investigated in 6 control and 6 treated Friesian cows, averaging 111 and 118 d postpartum in their fourth lactation of treatment. Each lactation the treated cows received sometribove injections (500 mg) every 2 wk (injection cycle) starting 60 +/- 3 d postpartum, increasing milk yield 3.3, 5.9, 1.9, and 4.2 kg/d in lactations 1, 2, 3, and 4, respectively. On d 8 of a fourth lactation injection cycle, blood was sampled for 390 min, starting 30 min before an intravenous glucose infusion (100 mg/kg) over a 20-min period. Preinfusion concentrations of glucose, insulin, and bST were elevated in sometribove-treated cows versus controls: 82.1 versus 74.4 mg/dl, 28.1 versus 19.7 microIU/ml, and 4.6 versus .9 ng/ml, respectively. Glucose infusion resulted in a rapid increase in blood glucose and insulin concentrations, followed by a sharp decline to preinfusion values across both treatments, resulting in similar net area under the curves for glucose and insulin. Blood bST concentrations remained unchanged. This study supports the concept that sometribove increases milk yield in dairy cows by chronically influencing homeorhetic mechanisms.     

Season and treatment effects on serum prolactin and milk yield during induced lactation

Nineteen nonpregnant, nonlactating dairy cows were allotted to three treatments to induce lactation during winter, 1976, or spring, 1977. All groups received 17 beta-estradiol (.1 mg/kg) days 1 to 7. Groups 2 and 3 also received progesterone (.25 mg/kg) days 1 to 7. Groups 1 and 2 were given reserpine (5 mg intramuscular) on days 8, 10, 12, and 14. Group 3 received reserpine (5 mg intramuscular) on days 2, 5, 8, 11, and 14. Blood samples were collected for prolactin analysis just prior to and 3 h after reserpine injection. Mean daily temperatures were 11.9 C for spring group and -6.5 C for winter group. Comparisons of spring with winter for basal prolactin concentrations, reserpine-stimulated prolactin concentrations, and 100-day milk yields were 44 with 10 ng/ml, 482 with 199 ng/ml, and 1991 with 862 kg. Differences in prolactin concentrations and milk yields among hormone and reserpine treatments could not be detected, but cows on treatment 3 in the spring gave the largest yield of milk. Prolactin concentrations were correlated with milk yields among cows and among cows within seasons. Seasonal differences demonstrate the critical role of prolactin in the treatment to induce lactation.     

Glucocorticoids in mammary secretions and blood serum during reproduction and lactation and distributions of glucocorticoids, progesterone, and estrogens in fractions of milk

Concentrations of glucocorticoids were measured in milk and blood serum during the estrous cycle, prepartum, parturition, postpartum, and early and late lactation. Glucocorticoids in milk did not change during the estrous cycle, averaging .35 ng/ml whereas they averaged .50 ng/ml prepartum, 3.08 ng/ml at parturition, and .50 ng/ml 1 wk postpartum. Glucocorticoids in milk declined from .59 ng/ml to .25 ng/ml as lactation advanced from 1 to 10 mo. Concentrations of glucocorticoids in blood serum were approximately 8 to 10 ng/ml during all reproductive states. There was no positive relationship between percentage of milk fat and concentrations of glucocorticoids in milk. Cortisol was the predominant glucocorticoid in serum; in milk corticosterone concentrations exceeded those of cortisol. Glucocorticoids, being more polar, had higher affinity for the nonlipid portion of milk; in contrast, progesterone, estradiol 17beta, and estrone were located predominantly in the lipid fraction of milk.     

Hormone induced lactation in the bovine III. Dynamics of injected and endogenous hormones.

Three lactations were induced in two cows in two trials by twice daily subcutaneous injections for seven days. Each injection contained .05 mg/kg body weight of estradiol-17beta and .125 mg/kg body weight of progesterone. Included with the hormones in trial 1 was a combination of 233 muCi of [6,7-hydrogen-3] estradiol-17beta and 12 muCi of [4-carbon-14] progesterone. During trial 2,2050 muCi of [2,4,6,7 hydrogen-3] estradiol-17beta were incorporated with the hormones for one cow and 2344 muCi of [1,2,6,7 hydrogen-3] progesterone for the other. Radioactivity from hydrogen-3 and carbon-14 was detected in urine and feces but not in mammary secretion during trial 1. Isotope recovery from [hydrogen-3] estradiol-17beta was too low to quantify. By day 17, 90% of the carbon-14 from progesterone was accumulated in feces and 8.0% in urine. For trial 2, recoveries of radioactivity by day 28 from urine, feces, and mammary secretions were, respectively, 32.4, 56.2, and less than .002% from [hydrogen-3] estradiol-17beta and 6.0, 87.7, and .25% from [hydrogen-3] progesterone. Estrogen and progesterone in plasma averaged 1.83 and 2.61 ng/ml during days 2 to 7. Estrogen decreased more rapidly than progesterone post-treatment, but both had decreased by days 16 to 19 when average prolactin of plasma increased. Quantitative measures of estradiol 17-beta and progesterone absorption, whether in plasma or excreta, were correlated.     

Initiation of parturition in dairy cows with dexamethasone. II. Response to dexamethasone in combination with estradiol benzoate.

Parturition was initiated in 26 Holstein cows given dexamethasone (4.4 mg/100 kg body weight) in combination with 25 mg estradiol benzoate intramuscularly at day 273 of gestation. Parturition occurred at 40.8 +/- 9.6 h after injection. Twenty-six control cows had an average gestation length of 281.5 days. Calving difficulty was not different although birth weight of calves was 2.5 kg less for induced cows compared with control cows. Severity of udder edema did not differ between groups. Average daily milk production for the first 9 wk of lactation was lower (24.2 versus 27.7 kg) from induced than control groups. Incidence of retained placental membranes was 50 and 4% for induced and control cows. Serum estrogens were lower (290 versus 601 pg/ml) in induced than in control cows 2 days prior to parturition. Groups did not differ inserum calcium, phosphorus, magnesium, days to first heat, days to first breeding, days to conception, or in fat, protein, and total solids content of colostrum. Casein in colostrum of induced cows was lower. Results of California Mastitis Tests at 15 and 30 days postpartum were similar.     

Prostaglandin in milk, days open, and estrus detection in dairy cows treated with prostaglandin F2 alpha

Prostaglandin F2 alpha was used to induce estrus in postpartum dairy cows to decrease calving interval and time spent on heat checks. The amount of prostaglandin residue in milk after treatment also was investigated. Twenty-two control cows, checked for heat twice daily, were bred at estrus after 55 days postpartum. Sixty-three cows checked on days 55 to 60 were either bred if in estrus or treated with 30 mg of prostaglandin F2 alpha injected intramuscularly on day 60 and bred at induced estrus or at 75 h posttreatment. Twelve cows were in heat between days 55 and 60 and were bred. Twenty-nine of 51 treated cows were seen in estrus; all of these were bred and 51.7% conceived at this time. Treated cows had fewer days to first service than did controls, but days open were not different, 105.7 versus 101.8. Fertility was similar. Controls required more heat checks than did treated cows (39 to 8.2). Milk from 17 cows at two milkings before and ten milkings after treatment had similar concentrations of prostaglandin (698 +/- 27 pg/ml) except for the first posttreatment milking when prostaglandin concentration almost doubled (1.293 +/- 143 pg/ml).     

Induced lactation in heifers: Effects of dexamethasone and age at induction on milk yield and composition

Milk production in heifers induced into lactation is lower than that of postpartum primiparous cows. A method to improve milk production in induced lactations may provide opportunities for increased profitability as well as increase our understanding of the mechanisms that regulate mammary gland development and colostrum composition. The present study was conducted to determine if dexamethasone administration at the onset of milking or age at lactation induction would affect milk production in heifers induced into lactation. Holstein heifers at 14 [n = 20; 354 ± 38 kg of body weight (BW)] and 18 mo of age (n = 20; 456 ± 30 kg of BW) were assigned randomly to dexamethasone (DEX) or control (CON) treatment groups in a 2× 2 factorial arrangement with age and dexamethasone treatment as the 2 factors. Heifers were induced into lactation with daily subcutaneous injections of estradiol-17β and progesterone (0.075 and 0.25 mg/kg of BW per d, respectively) on experimental d 1 to 7. They also received bovine somatotropin (bST) every 14 d beginning on experimental d 1. Milking began on experiment d 18 (lactation d 1). Dexamethasone (10 mg) was administered on lactation d 1 and 2 following the morning milking; CON heifers did not receive dexamethasone. Milk yield from d2 to 15 of lactation of heifers receiving DEX (7.8 kg/d) was greater than that of CON heifers (6.0 kg/d) but was similar thereafter through 305 d of lactation (18.2 kg/d). Milk production to d 11 was similar for 14- and 18-mo-old heifers but was greater for 18- (18.9 kg/d) than for 14-mo-old animals (17.4 kg/d) through 305 d in milk. Milk fat percentage increased initially and was greater in DEX (4.51%) compared with CON (3.53%) heifers until 21 d in milk. Milk protein and lactose concentrations were not affected by DEX treatment. Age at induction did not affect milk fat, protein, or lactose percentages. Mean milk IgG concentration declined from 107.4 mg/mL on d 1 to 5.0 mg/mL on d 7 of lactation, tended to be greater for 18- compared with 14-mo-old heifers, and was not different due to DEX treatment. Administration of DEX to heifers induced into lactation increased initial milk production during the first 2 wk of lactation but this effect did not persist through 305 DIM. Treatment with DEX appeared to stimulate mammary cell differentiation but did not change the rate of decline of milk IgG concentrations. Higher milk yield in 18-mo-old heifers may be due to greater mammary epithelium, higher body mass, or both.     

Effects of dietary glucogenic precursors and fat on feed intake and carbohydrate status of transition dairy cows

Twenty-four multiparous Holstein cows were used to determine the effects of dietary fat and glucose precursors on energy status and lactation. The treatment group (T) received 409 g/d (DM basis) of a combination of calcium salts of fatty acids, calcium propionate, and propylene glycol. The control group (C) received 409 g/d of a mixture of calcium salts of fatty acids and ground barley from 14 +/- 0.9 g/d before until 21 d after calving. Dry matter intake was greater (16.1 vs. 13.6 +/- 1.3 kg/d) for T than C during the last week prepartum and did not decrease for T from the previous week, whereas, in C, DM intakes decreased by 3.2 kg/d. Production of milk and milk fat did not differ. There was a tendency for lower protein and increased lactose concentrations in milk from T cows. Milk fat percentage was lower in T at d 7 (5.5 vs. 6.4 +/- 0.5%) and 28 (4.4 vs. 5.5 +/- 0.5%) of lactation. Liver lipid content was numerically lower (7.9 vs. 9.2 +/- 0.9%) and glycogen content was significantly higher (2.4 vs. 2.0 +/- 0.1%) in T vs. C cows on d 7 of lactation. Concentrations of nonesterified fatty acids were lower in blood of T cows on d 2 and 7 of lactation. Over all time points, blood glucose concentrations were higher in T cows pre- (70.75 vs. 62.1 +/- 1.3 mg/dL) and postpartum (60.1 vs. 56.2 +/- 1.1 mg/dL). Insulin concentrations in blood were greater for T (397 vs. 314 +/- 48 pg/mL) both pre- and postpartum. Feeding glucose precursors in combination with rumen inert lipids, compared with feeding barley in combination with the lipids for 2 wk before parturition and 3 wk postpartum helped avoid prepartum feed intake depression and increased blood glucose and insulin and decreased blood NEFA.