Figure 1. Mean energy balance for treatment and control groups during the first six weeks postpartum.
S. Miyoshi, J.L. Pate, and D.L. Palmquist
Department of Animal Sciences
We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve reproductive status. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was drenched orally with 8 ounces of propylene glycol each day from 7 to 42 days of lactation. Blood samples were collected, and cows were rectally palpated three times per week until 11 weeks. Propylene glycol did not affect feed intake or milk yield but tended to increase energy balance in multiparous cows. After drenching, propylene glycol increased plasma glucose and insulin. Propylene glycol decreased days to first ovulation (31 vs 45) and tended to increase plasma progesterone; the length of the first luteal phase was longer in treated cows. The number of days open was 16 days shorter in treated cows, and services per conception tended to be lower. Conception rate at first insemination was twice as high in treated cows as in control cows. Although few treatment effects for reproduction measures were significant, all trends were toward improved reproductive performance with propylene glycol. The data are consistent with an important role for insulin in ovarian activity in early lactation.
Peak milk production occurs earlier than maximal dry matter intake (DMI), causing cows to be in negative energy balance and to mobilize body fat in early lactation. Insufficient energy intake relates to poor reproductive performance and prolonged postpartum anestrus, lower levels of progesterone production by the corpus luteum, and low rates of conception. Previous studies showed that negative energy balance in early postpartum affected follicular development and increased the interval to first ovulation (Butler and Smith, 1989). Also, low concentration of insulin in plasma is associated with negative energy balance in the early postpartum period; this important metabolic hormone stimulates follicular development and corpus luteum function. University of Wisconsin researchers showed that 36 ounces of propylene glycol drenched orally to cows increased plasma concentration of glucose and insulin and decreased concentration of fatty acids in blood from adipose mobilization (Studer et al., 1993). We studied the relationships among energy balance, blood glucose, plasma insulin, and ovarian function when cows were drenched daily with 18 ounces of propylene glycol.
After calving, 36 Holstein cows divided into two groups of 18 cows (10 first lactation in each group) were fed a standard herd ration. One-half of the cows were drenched daily with 18 ounces of propylene glycol (Texaco, Inc., Feed Houston, TX) from 7 to 42 days of lactation. composition and intake, and milk yield and composition were monitored daily. Blood samples were taken, and cows were palpated three times per week for 11 weeks.
Propylene glycol did not change dry matter intake, milk yield, or milk composition (percent fat and protein), whereas energy balance was slightly improved for multiparous cows during the first 42 days of lactation (Figure 1).
After drenching with propylene glycol, plasma glucose and insulin concentrations increased rapidly by 30 minutes and continued to increase gradually to 90 minutes, whereas plasma fatty acid concentration decreased. With multiparous cows, energy balance of treated cows was less negative, and days to first ovulation was 8 days earlier. With primiparous cows, energy balance was similar between treatments. Days to first ovulation of the treated primiparous cows, however, were 18 days shorter than that of controls. Energy balance in early postpartum was correlated positively with plasma insulin concentration, which was related to days to first ovulation. No relationship was observed in later estrous cycles. Importantly, first postpartum ovulation occurred earlier in treated primiparous cows, even though energy balance was not different between treatments. Thus, increased plasma insulin in treated cows may have had direct effects on follicular development and LH secretion in the early postpartum period.
Britt (1992) suggested that follicular growth may be affected by severe negative energy balance during the early postpartum period, and that could cause low progesterone secretion in the third, fourth, and fifth estrous cycles. In Britt's model, negative energy balance has delayed effects on luteal function. However, in our study, only the first luteal phase was affected by treatment. Days to first progesterone peak was 8 days shorter, and cumulative plasma progesterone concentration of the first estrous cycle was 46% greater in treated cows, whereas smaller changes were observed for later cycles. University of Florida researchers showed that growth of preovulatory follicles can be affected by acute short-term changes in energy balance (Staples et al., 1990; Lucy et al., 1991), and Ohio State University researchers found that insulin is necessary for maximal progesterone production by bovine luteal cells (Haq and Pate, unpublished). In our study, plasma insulin concentration and days to first progesterone rise were related. Greater corpus luteum function of treated cows may be explained by improved energy balance and higher plasma insulin concentration after drenching, which may have increased progesterone synthesis. Therefore, insulin may be an important factor in reestablishment of ovulatory cycles postpartum. The reestablishment of ovulatory cycles, obtaining positive energy balance, and increasing plasma insulin concentration as soon as possible postpartum is important. In our study, ovarian activity in the first estrous cycle was greater in treated cows than in control cows. Presumably, this was because follicular development and corpus luteum function were affected immediately and directly by higher energy balance and insulin concentration. Further, the number of days open was shorter in treated cows, and conception rate at first service was twice as high in treated cows. This may have been influenced by earlier cycling in treated cows. Thus, all results taken together support the hypothesis that propylene glycol improves reproductive performance in early lactation (Table 1).
Figure 1. Mean energy balance for treatment and
control groups during the first six weeks postpartum.
| Table 1. Summary of important trends from drenching cows with 18 ounces of propylene glycol from 7 to 42 days of lactation. | ||
| Parity | ||
| Item | Primiparous | Multiparous |
| Energy | ||
| DMI | No effect | No effect |
| 4% FCM | No effect | No effect |
| Energy balance | No difference | More positive |
| Plasma measures | ||
| Glucose | Increase | Increase |
| Insulin | Increase | Increase |
| NEFA | Decrease | Decrease |
| Ovarian function | ||
| Days to first ovulation | Earlier | Earlier |
| Days to progesterone rise | Earlier | No difference |
| Length of first luteal phase | Longer | Longer |
| Total progesterone | Greater | Greater |
| Reproductive performance | ||
| Conception rate at first service | Higher | Higher |
| Days open | Shorter | Shorter |
Because drenching had a direct effect on ovarian function, it may be sufficient to drench only during the first three weeks of lactation, thus inducing early cycling and reducing the costs associated with drenching. An alternate useful strategy may be to drench for one week prior to insemination, especially for cows that are in poor estrous status.
Grummer et al. (1994) found that a daily dose of 10 ounces of propylene glycol was nearly as effective as 32 ounces to reduce lipid mobilization during restricted feed intake.
However, the insulin response to 10 ounces was smaller than for 32 ounces. Ten ounces of propylene glycol may not be adequate to increase insulin concentration and ovarian activity. Dose-responsiveness for cost-effective therapeutic treatment of early postpartum cows remains to be investigated. Top dressing propylene glycol on the feed may cause reduced feed intake, that will probably lessen its benefits. Until feeding strategies are developed, drenching is the method of choice.
This project was funded in part by a research grant provided by the Ohio Dairy Farmer's Research Fund.
Britt, J. H. 1992. Impacts of early postpartum metabolism on follicular development and fertility. The Bovine Practitioner Proc. 24:39.
Butler, W. R., and R. D. Smith. 1989. Interrelationships between energy balance and postpartum reproductive function in dairy cattle. J. Dairy Sci. 72:767.
Grummer, R. R., J. C. Winkler, S. J. Bertics, and V. A. Studer. 1994. Effect of propylene glycol dosage during feed restriction on metabolites in blood of prepartum Holstein heifers. J. Dairy Sci. 77:3618.
Haq, I., and J. L. Pate. 1992. Actions of insulin and growth hormone on the corpus luteum. (Unpub.)
Lucy, M. C., C. R. Staples, F. M. Michel, and W. W. Thatcher. 1991. Energy balance and size and number of ovarian follicles detected by ultrasonography in early postpartum dairy cows. J. Dairy Sci. 74:473.
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