Milk ejection in primiparous heifers in the presence of their calves

Milk production and anatomical udder capacity changes of udder halves subjected to increased milking frequency at two stages of lactation

This study aimed to characterize the effects of increased milking frequency (IMF) at early and mid-lactation on milk yield and its association with changes in cistern and alveolar capacity. Fourteen multiparous Holstein cows were subjected to IMF using the unilateral frequent milking method from 3 to 24 d in milk (DIM). At mid-lactation, cows were randomly assigned to 1 of 2 treatments: control or repeated. From 150 to 170 DIM, IMF treatment was reimposed in the repeated group. During IMF, left udder halves were milked 2× and right udder halves were milked 4× daily. To separate individual milk yields of udder halves, separate buckets were used to collect samples from each udder half. Milk samples and milk yield from right and left udder halves were collected on d 150, 170, 200, 230, 260, and 290 of lactation. Alveolar and cistern capacity were measured 26 h after the last milking at 140 and 172 DIM using an oxytocin inhibitor. Cistern and alveolar capacity were measured by evaluating the milk harvested after oxytocin inhibitor and oxytocin administration, respectively. Udder half difference yields were calculated by subtracting left half yield from right half yield. At 170 DIM, the udder half difference in repeated was 2.27 kg greater than the udder half difference in control. Udder halves milked 4× produced more milk and protein than 2× udder halves in the repeated group at 170, 200, 230, and 260 DIM. Cumulative (150 to 290 DIM) and carry over (200 to 290 DIM) udder half differences in milk yield were similar between the control and repeated treatments. Alveolar volume was similar between udder halves milked 2× or 4× at 140 DIM, while cistern volume was larger for udder halves milked 4× than 2× in early lactation. There was no difference between alveolar or cistern volume proportion in udder halves milked 2× or 4× before mid-lactation IMF. After 20 d IMF for the repeated group, alveolar volume was similar between control and repeated independent of udder half milking frequency. However, repeated held 4.9 kg more cistern milk than control. Control treatment udder halves had a greater alveolar proportion than repeated treatment udder halves. As expected, the cistern proportion was smaller in control and larger in repeated after mid-lactation IMF. IMF at early and mid-lactation enhances milk and protein yield largely during differential milking frequency regimens. The lack of enhancement in milk yield after IMF might be associated with a different response to IMF in the mammary gland at early versus mid-lactation. Based on our results, we conclude that udder halves subjected to early and mid-lactation IMF had increased cistern volume capacity.

Milk Leakage—An Increased Risk in Automatic Milking Systems

Milk leakage (ML), or milk observed dripping or flowing from one or more teats between milkings, has been associated with increased risk of udder infections and mastitis in dairy cows. Preliminary observations indicate that ML might occur more often in automatic milking systems (AMS) than in conventional milking systems (CMS), but comparative data on the incidence of ML in AMS or in CMS are not available. Therefore, the occurrence of ML at various observation periods was studied in one AMS with cows housed in a free-stall barn in comparison to CMS with cows housed either in a free-stall barn or a tie-stall barn and milked at regular intervals in a herringbone milking parlor. Relationships between ML and other cow and management factors were also examined. In each of 2 yr, all cows (n = 230 total; 46 cows present both years) were observed at 2-h intervals during six 24-h periods. At least one ML occurred in 39.0 (AMS) vs. 11.2% (CMS) of individual cows and in 16.2 (AMS) vs. 2.9% (CMS) of 24-h cow days studied. Milk leakage was not related to milk production, parity, stage of lactation, or estrous status. However, in the AMS, 62% of primiparous and 28% of multiparous cows leaked milk at least once. Milk leakage occurred more often in rear than in forequarters. Cows were usually lying down when ML was observed, but intervals from previous milking varied, especially in AMS. In AMS, about one-fifth of the ML observations occurred < or = 4 h after milking, and half of those were associated with disturbances at the previous milking. Milk flow rate was higher in quarters leaking milk than in other quarters. Strategies to reduce milk leakage in AMS may be important to minimize potential risks of udder disease.

Postpartum acyclicity in suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows is a source of economic loss to beef cattle producers. Duration of postpartum acyclicity is influenced by suckling status, nutritional status, calving season, age, and several other factors. Although uterine involution begins and ovarian follicular waves resume soon after parturition, dominant follicles of these waves fail to ovulate, due to a failure to undergo terminal maturation. As a result, postpartum anovulatory dominant follicles are smaller than the ovulatory follicles in cyclic cows. Failure of postpartum dominant follicles to undergo terminal maturation is due to absence of appropriate LH pulses, a prerequisite for follicular terminal maturation prior to ovulation. Absence of LH pulses early post partum is primarily due to depletion of anterior pituitary LH stores, although GnRH pulses are also absent during this period due to suckling. Following replenishment of LH stores between Days 15 and 30 post partum, absence of LH pulses is due to continued sensitivity of the hypothalamic GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta, which results in absence of GnRH pulses. This negative feedback effect of estradiol-17beta is modulated by suckling which stimulates release of endogenous opioid peptides from the hypothalamus. As the postpartum interval increases, sensitivity of the GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta decreases. This is followed by an increasing frequency of GnRH discharges and LH pulses, terminal follicular maturation, ovulation, and continued cyclicity. The first ovulation post partum is usually followed by a short cycle due to premature luteolysis because of premature release of PGF2alpha from the uterine endometrium, which is possibly intensified by the suckling-induced oxytocin release from the posterior pituitary. A model for the postpartum ovulatory acyclicity and for the resumption of cyclicity is presented.