Composition	(% of DM)
Ingredient
Grain	44.0
Soybean seed meal	6.4
Rape seed meal	3.4
Com gluten meal	3.4
Cotton seeds	8.8
Vetch hay	4.3
Wheat silage	25.5
Vitamin and mineral mix	4.2
Chemical
DM	51.8
CP	17.0
ADF	16.1
NDF	29.0
NEl,Mcal/kg	1.7

‘Each kilogram of mix contained 4,000,000 IU of vitamin A, 400,000 IU of vitamin D, 3000 IU of vitamin E. 12 mg of Mn. 12 mg of Zn, 4 mg of Fe, 240 mg of 12. 40 mg of CO, 100 mg of Se, 800 mg of Cu, 1.4 mg of (NH4)2SO4. 1 mg of MgS04. 180 mg of Ca. 90 mg of P, and 90 mg of NaCI.

mination of the day of calf intake detected no systematic difference with other days of the week (P > .05). Milk samples were collected at each milking 1 dwk for 18 wk PP. For cows on the S treatment, milk was sampled only at machine-milking during the first 6 wk PP. Milk composition was determined by the central laboratory of the Israel Cattle Breeders’ Association (Bitan Aharon), and fat content was used to determine 4% FCM. Total milk production for the lactation and composition data were available from the same source based on monthly recordings.

Cow BW was recorded weekly for 18 wk PP, starting 2 wk before calving. Calving BW and BW at 3 d PP were averaged and used as initial BW. The correlation coefficient between initial BW and precalving BW was .992 (P c .05). Body condition scores (BCS) were assessed weekly for 18 wk, starting 1 wk before calving. One person ranked cows for BCS on a five-point scale (1 = emaciated to 5 = obese).

Feed intake for the first 10 wk was determined daily for each individual cow. The DM content of the feed and orts was determined by weekly analysis. Nutrient content of ration components was determined by weekly sampling and ration analysis

An indwelling cannula was placed in the jugular vein 24 h prior to blood sampling. Samples of venous blood (10 ml) were drawn from the cannula into heparinized syringes and immediately processed (centrifugation at 1000 x g for 10 min at 4°C) for collection of plasma, which was then stored at -20°C until analysis. Samples were collected at intervals of 30 min, commencing at 0600 h and finishing at 1300 h. For practical reasons, samples could not be taken during milking, so pre- and postmilking (or pre- and postsuckling) samples were taken at approximately 5 min before and 10 min after milking or suckling. The procedure was performed at wk 1 PP (d 7 of lactation for each cow) and repeated at wk 6 and 10 PP

Hormone Analyses Hormones were measured by specific double-antibody radioimmunoassays: growth hormone (GH), prolactin, and insulin as described by Vernon et al. (32); IGF-I after acid-ethanol extraction as described by Daughaday et al. (10); and oxytocin after extraction as described by Stock and Uvans-Moberg (29).

Statlstlcal Analyses

All statistical analyses were carried out using the general linear models procedure of SAS (28). Weekly data for milk production, FCM, DMI, BW change, and BCS were compared over treatments, weeks PP, and initial BW by analysis of variance, using cows within treatment and BW as the error terms for comparisons among treatments. The models also included an interaction effect of treatment and week PP.

Significance was set at P c .05 unless noted otherwise, and individual comparisons of treatments were made by Tukey’s Studentized multiple comparison test. Each of these models was tested separately for wk 1 to 6 PP and wk 7 to 18 PP. For each of wk 1, 6, and 10 PP, hormone measurements over 7 h were aggregated by calculating the area under the curve; those values were compared over weeks and groups by two-way analysis of variance, using variance among cows within groups as the error term for group comparisons. When interaction was significant, oneway analysis of variance was performed for each week separately.

RESULTS

Milk production is shown in Figure 1, and mean values by period are shown in Table 2.

Figure 1. Milk production of cows milked three times daily (M3; m), six times daily (M6; A), or milked three times daily and suckled three times daily (S; 0, 0) during the fmt 6 wk of lactation. Production of cows in the S group for total lactation (0) and machine-milkng only (0). Values are means with representative standard errors of the mean. Other standard errors of the mean are omitted for clarity.

During the treatment period, differences among groups were significant; milk production of cows in the S group was highest, and that of cows in the M3 group was lowest. Milk production was still increasing at wk 6 for cows in the S and M6 groups, but peaked during wk 4 for cows in the M3 group. Figure 1 also shows the amount of milk obtained at machine-milking for cows in the S group. This amount increased for the first 2 wk PP but then decreased; at its peak, machine-milking represented 40.7% of total production and, by wk 6, had fallen to 23.5%.

Milk production decreased sharply in wk 7 (immediately posttreatment) for cows in group S and, to a lesser extent, for cows in group M6; decreases were 29.2 It 1.18 and 4.6 It .62 kg/d, respectively. Despite these results, cows in the M6 group continued to produce more milk than cows in the M3 group (13.6%). Values for milk production of cows in the S group increased between wk 7 and 8 and more slowly thereafter, remaining lower than those for cows in the M3 group until wk 10 and then stabilizing after wk 12 before converging with values for the milk production of cows in group M6 at wk 18. Overall, milk production during wk 7 to 18 PP was similar for cows in the S and M3 groups but significantly higher for cows in the M6 group

Milk fat and protein contents were similar for all groups during the treatment period except for a reduced fat content of milk produced by cows in the S group compared with that for milk produced by cows in the M3 group (Table 2). Consequently, fat and protein yields were higher for cows in the M6 group than for cows in the M3 group, and the calculated values for cows in the S group were higher still, although component yields were probably underestimated because they were based on composition measured at machine-milking only. Fat content was greater in milk obtained later in milking, and the calves removed milk more efficiently than did the milking-machines. No posttreatment differences were found for milk fat or milk protein percentages. The DMI was significantly higher for cows in the M6 group than for cows in either the M3 or S groups throughout treatment and for the first 3 wk

TABLE 2. Milk production (MP), milk composition, DMI, and BW loss of cows milked three times daily (M3). six times daily (M6). or milked three times daily and suckled three times daily (S) during the first 6 wk of lactation.’

M3 M6 S P > F
	X-	SEM	X-	SEM	X-	SEM
wk 1 to 6 Postpartum
MP, kg/d	35.30	.80c	42.61	.20b	50.00	1.30a	**
Fat,%	3.28	.05a	3.16	.08ab	3.07	.09b	*
Protein,%	3.13	.04	3.07	.07	3.01	.08	NS2
Fat, kg/d	1.15	.03c	1.34	.06b	1.53	.09a	*
Protein,kg/d	1.10	.04c	1.30	.07b	1.50	.07a	*
4% FCM, kg/d	31.48	.70c	37.23	1.00b	43.00	1.10a	*
DMI,kg/d	16.80	.70b	19.40	.50a	16.20	.40b	*
BW Loss,kg/d	-0.60	.03c	-0.75	.02b	-1.40	.04a	*
wk 7 to 18 Postpartum
MP,kg/d	37.40	.40b	42.50	.50a	37.50	.60b	**
Fat,%	2.80	.01	2.81	.03	2.82	.03	NS
Protein,%	2.76	.02	2.79	.03	2.82	.03	NS
4%, FCM ,kg/d	30.66	.90b	34.91	.80a	30.86	.70b	*
DMI,kg/d 3	20.10	.70b	22.40	.50a	19.00	.30b	*

a.b,cMeans within rows with different superscripts differ P < .05. ‘For M3 and S. n = 10; for M6, n = 9. 2P > .05. 3Mean DMI for wk 7 to 10. *P < .05. **P < .01.

(Figure 2. The DMI of cows milked three times daily (M3; B), six times daily (M6; A), or milked three times daily and suckled three times daily (S; 0) during the first 6 wk of lactation. Values are means with representative standard errors of the mean. Other standxd errors of the mean are omitted for clarity.)

posttreatment; by wk 10, values were similar for all groups Figure 2 and Table 2). The DMI of cows in the S group were similar to DMI for cows in the M3 group during treatment and somewhat lower during the first 3 wk posttreatment (Figure 2).

The mean initial BW were very similar for the three groups (overall mean, 563 kg). During the first 6 wk PP, the cumulative BW loss was -25.2, -31.5, and -58.8 kg, for cows in the M3, M6, and S groups, respectively, which was significantly greater for cows in the S group than for cows in either the M3 or M6 groups (Figure 3a). The cows in the M3 and M6 groups reached their lowest BW at wk 5 and 6 PP and recovered to reach calving BW in the 12th and 15th wk PP, respectively. However, cows in the S group continued to lose BW until wk 8 PP, 2 wk after removal of the calves, and calving BW was not attained until wk 18 PP (Figure 3a).

Initial BCS were also very similar for the three groups (overall mean, 2.67). Decreases for the first 6 wk PP for cows in the M3, M6, and S groups, respectively, were greater (P < .Ol) for both the M6 and S groups than in the M3 group (Figure 3b). The BCS of cows in the M3 and M6 groups stopped decreasing during the 7th wk PP. However, for cows in the S group, BCS continued to decrease until the 11th wk PP, and only then started to recover.

Hormone data are presented in Figure 4. For all hormones studied, profiles were very similar at wk 1 and 6, so data were plotted for wk 1 and 10 only. Calculated values for areas under the curves are presented in Table 3. During treatment, basal values for oxytocin (those samples taken between milkings or sucklings) were highest for cows in the S group, intermediate for cows in the M6 group, and lowest for cows in the M3 group. The greatest oxytocin release was observed for cows in the S group as a response to suckling; cows in all three groups demonstrated a smaller pulse release 10 min after the afternoon milking, and little difference existed among groups in this regard. Oxytocin area under the curve was significantly higher for

Figure 3. Change in BW (a) and body condition score (1 = emaciated and 5 = obese) (b) of cows milked three times daily (M3; B), six times daily (M6; A), or milked three times daily and suckled three times daily (S; 0) during the first 6 wk of lactation. Values are means with representative standard errors of the mean. Other standard errors of the mean are omitted for clarity.

VERY FREQUENT MILKING OR SUCKLING

Figure 4. Plasma hormone concentrations of cows milked three times daily (M3;-), six times daily (M6; _ _ _ _ _ ), or milked three times daily and suckled three times daily (S; . . . . .) during the first 6 wk of lactation. Values are means. Samples were taken at intervals of 30 min during 7 h and additionally at 5 min before and 10 min after milking or suckling. Cows in the M6 and S groups were milked or suckled at 0700 h, and all cows were milked at 1200 h.

cows in the S group than for cows in the M6 or M3 groups. Oxytocin did not change posttreatment for cows in the M3 group, but, in the S group, the basal values were lower than during treatment. The postmilking peak was similar to premilking values, but a morning peak no longer existed, because suckling was absent. Oxytocin area under the curve was significantly lower postmilking for cows in the S group than for cows in the M3 group (Table 3)

Prolactin varied during the day during all 3 wk. Cows in the S group exhibited a clear pulse of prolactin release at suckling (wk 1 and 6; data shown for wk 1 only), but there was no clear postmilking release at any time in any group. Area under the curve was highest for cows in the S group (P e .05). intermediate for cows in the M6 group, and lowest for cows in the M3 group during treatment.

Clear differences existed in GH concentrations among the groups during treatment. Area under the curve values confirmed that concentrations of GH were elevated in cows in the S group compared with cows in the M6 group (P < .OS); GH concentrations were lower (nonsignificantly) for cows in the M3 group than for cows in the M6 group. By wk 10, GH values were no longer significantly different among groups. Differences in IGF-I among groups reflected the differences in GH, but the higher IGF-I values of cows in the S group were significant for all 3 measurement wk (Table 3). Insulin concentrations demonstrated the reverse; insulin was highest in cows in the M3 group, intermediate in cows in the M6 group, and lowest in cows in the S group throughout (Table 3)

DISCUSSION

Increasing milking frequency from 3 to 6x raised milk production by 7.3 kg/d (21%) during the first 6 wk PP. Previous studies of increased milking frequency have mainly involved increases from 2 to 3x, and milk production increases of from 6 to 25% have been observed (3, 11, 23). The present data clearly indicate that milking 3x does not result in maximum production. To our knowledge, this experiment was the first detailed study of protracted, very frequent milking during early

(TABLE 3. Plasma hormone concentrations (ma under the curve) of cows milked three times daily w3), six times daily (M6). or milked three times daily and suckled three times daily (S) during the first 6 wk of lactation, determined from 30-min spaced samples taken over 7 h.

M3 M6 S P
	X-	SEM	X-	SEM	X-	SEM
wk 1 Postpartum							*
Oxytocin	67.5	12.1b	82.1	11.4b	168.9	31.1a	*
Prolactin	491.6	27.1c	646.5	42.7b	784.7	47.2a	*
GH1	22.5	4.2b	30.2	3.9b	39.8	4.7a	*
IGF-1	580.2	186.2b	976.7	240.6b	1932.9	415.2a	*
Insulin	7.1	.7a	5.5	1.1a	2.1	2.1b	*
wk 6 Postpartum							*
Oxytocin	101.1	15.3b	122.1	13.7b	217.6	28.7a	*
Prolactin	636.6	49.5b	724.1	52.7b	922.6	75.2a	*
GH	19.1	2.1b	21.5	2.9b	30.6	3.6a	*
IGF-1	343.1	86.2b	543.1	134.5b	921.0	178.4a	*
Insulin	12.1	1.3a	9.2	1.8a	5.8	1.4b	*
wk 10 Pstpartum							*
Oxytocin	100.9	14.7b	123.6	21.4a	66.5	13.2c	*
Prolactin	156.9	19.5b	192.2	22.7ab	216.3	15.4a	*
GH	14.7	.7	16.1	.8	17.0	2.3	NS
IGF-1	223.7	46.2b	286.7	34.7b	397.3	62.4a	*
Insulin	18.0	1.3a	11.7	2.1b	10.0	2.8b	*

————–table page=7————a.b.cMeans within rows with different superscripts differ (P <.05) ‘Growth hormone. *P <.05.)

lactation. Other studies, which have been brief (31) or have been conducted using unmatched groups of cows at different stages of lactation (15), reported increases of 8 to 10%. Milking 4x for 4 wk increased milk production by 11% above milking 2x (14), but, once again, this response was submaximal; other cows milked 4x and additionally treated with GH (recombinant bST) increased production by 28% (18). The difference between cows in the M6 and M3 groups quite possibly would have increased further if treatment had continued; milk production was still increasing for cows in the M6 group at wk 6 PP, but for cows in the M3 group, production showed no real increase after wk 4.

Some effects of very frequent milk removal could be mediated by endocrine factors related to teat stimulation, particularly oxytocin, prolactin, and GH. Evidence exists that different forms of teat stimulation affect hormone release in distinctive ways (13) and that calf presence can affect the response of a cow to teat stimulation (2). Detailed mechanistic studies require very frequent sampling around milking, which we did not attempt; nevertheless, some endocrine differences were apparent. Oxytocin and prolactin values were higher in cows from the S group, intermediate in cows from the M6 group, and lowest in cows from the M3 group. Oxytocin differed largely as a consequence of additional postmilking and suckling release, but prolactin differences were mainly because its baseline was higher for the S and M6 groups than for the M3 group. The recognized action of oxytocin is in milk removal. Recent claims that oxytocin can stimulate mammary metabolism (5) have not been supported by analysis of data from half udders within cows, which demonstrated that oxytocin administration increased production in the half udder that was milked just after injection but not in the contralateral half, which was milked earlier (16). In the present experiment, we observed a posttreatment depression in basal oxytocin concentrations of cows in the S group, but no reduction in the postmilking surge. We suggest that this effect would have little biological consequence for milk production. Long-term treatment with oxytocin improved lactation persistency of dairy cows (21), but it is not known whether this was an effect of the hormone per se or a consequence of improved milk removal.

Although prolactin is essential for successful lactation in rodents, no evidence exists of any galactopoietic effect during established lactation in ruminants (24). An increase in mammary growth and differentiation during the early lactation treatment phase may explain the long-term effects on milk production. Once again, although prolactin was implicated in mammary growth control of nonruminants, the evidence for ruminants did not support a mammogenic role for prolactin (9).

One hormone that is clearly implicated in galactopoiesis 0 and also in mammogenesis (9) is GH. Differences in GH concentrations among groups corresponded to milk production: highest GH and milk production for cows in the S group and lowest GH and milk production for cows in the M3 group. Milk production might have responded to GH; however, the GH differences just as easily could have been a consequence of the energy status of the three groups. Our results do not rule out a subsequent effect of GH on milk production, but this experiment provided no evidence of a causative action. During wk 1, GH release was related to the afternoon milking. This release was not repeated in other weeks, and could have represented enhanced responsiveness of the GH axis early in lactation.

Because frequent milking of one half of the udder affects only that half (14), the main effect of milking frequency is not related to endocrine function, but is directly related to actual milk removal. This result is due to the presence of a protein in milk that inhibits milk secretion, the feedback inhibitor of lactation (FIL) (33). As milk accumulates in the udder between milkings, secretion rate gradually decreases because of the action of FIL. More frequent removal of milk thus enables a longer maximal secretion rate. The main effect of FIL is exerted during protein secretion (26), resulting in an immediate reduction in milk production. The FIL directly inhibits mammary differentiation in vitro (35), so the positive effects of frequent milking on mammary differentiation are probably also mediated in this way.

The data demonstrated a clear carry-over effect of very frequent milking early in lactation. Production did decrease when frequency was reduced from 6 to 3x, but, during 12 wk posttreatment, cows in the M6 group still produced 5.1 kg/d (13.6%) more than cows in the M3 group, a significant difference. The milk production for the entire 305-d lactation was significantly higher for cows in the M6 group (10,476 f 397 kg) and S (9897 f 47 1 kg) groups than for cows in the M3 group (8994 rt 260 kg). Milk composition was not different among groups, and lactation fat and protein yields increased. Although others (23, 25) have demonstrated carry-over after periods of milking 3x, the effects were small and not statistically significant. This difference in results might be related to the fact that our experiment was the first time that treatment had been applied so early in lactation. The presence of a carry-over effect implied that mammary development had been enhanced. Frequent milking has been shown to increase both mammary differentiation and proliferation of mammary cells of goats (36) and of cows (14). Because mammary proliferation continues for the first few weeks PP at least in goats (19), the mammary gland may well be exquisitely responsive to mammogenic stimuli during early PP (1).

A further novel finding of the present study was the higher total milk production of suckled and milked cows versus very frequently milked cows. The mechanism underlying this difference is unknown. Earlier studies (12, 30) investigating low frequency of udder emptying established that suckling stimulated higher milk production than did machine-milking. In our experiments, we used two heifer calves suckling 3x to ensure a maximum stimulation. Endocrine profiles were different for cows in the S group compared with cows in the M6 group, but perhaps the calves emptied the udder particularly well, thus further reducing the inhibitory action of FIL. However, machinemilking removed relatively little milk from cows in the S group; presumably milk ejection was voluntarily suppressed to ensure milk for the calves. Thus, three of the six milk removals were efficient (calf suckling), and the other three were inefficient (machine-milking). Inefficient milking reduced milk production of goats locally through FE action (M), and the reason that overall production was significantly higher for cows in the S group remains unknown.

The suckling stimulus was abruptly removed at the end of the 6-wk treatment period. As a consequence, milk production dropped very markedly for cows in the S group, and, during the 1st wk posttreatment, cows in the S group gave little more milk at machinemilking than they had when they were still feeding calves. This result was almost certainly due to psychological disturbance of milk ejection (i.e., poor milk removal) rather than to a direct inhibition of milk secretion per se. The FIL mechanism would thus have operated to restrict secretion to an amount appropriate to the reduced overall milk removal. As the cows became more accustomed to the absence of the calves, milk removal improved, and milk production increased, rising above the production of cows in the M3 group to a production very similar to that of cows in the M6 group. Suckling during early lactation apparently induced the same mammary developmental improvements as very frequent milking, but expression of the improved production was delayed following calf removal until the cow adjusted to the changed conditions. The period of inefficient milking immediately after calf removal had no long-term deleterious effect on milk production, which was in agreement with recent observations of short periods of once daily milking in cows (17).

Increased milk production has an energy cost. Thus, cows in the M6 group consumed more DM than did cows in the M3 group. In some studies (27), a measurable increase in DMI accompanied the rise in milk production from higher milking frequencies but, in other studies, the increase was too small to be measurable or nonexistent (3, 11). The increased DMI by cows in the M6 group did not compensate for the increased energy demands, and thus these cows lost more BW, had a lower BCS during the initial lactation period, and displayed a longer recovery period than did cows in the M3 group. Despite this occurrence, health parameters (mastitis or lameness) were not observably different among the groups.

The lower BW of cows in the S group was not initially reflected in a decreased BCS, which fell by similar amounts for cows in the S and M6 groups PP. Curiously, cows in the S group did not increase DMI over that of cows in the M3 group, and cows in the S group ate significantly less than did cows in the M6 group even though access to feed was unlimited for both groups. This result was unexpected and is a major area for further study. Why cows in the S group ate less is not known. The different endocrine profiles of cows in the S group allow for some speculation, particularly with regard to the possible role of elevated plasma oxytocin [oxytocin suppressed voluntary feed intake of rats (4, 22)]. However, it is not yet possible to draw any firm conclusions. Health status did not appear to be affected; cows in the S group had no greater incidence of mastitis or lameness than did cows in the M3 or M6 groups and had the best conception rates of the three groups, although reproductive activity of the cows in the S group was totally suppressed until after calf removal (U. Bar-Peled, 1994, unpublished data).

CONCLUSIONS

We have demonstrated that frequent udder emptying during early lactation has short and long-term effects on milk production. Suckling produced a greater short-term increase than milking did, but the carry-over effect was then delayed by the psychological disturbance of calf removal. The DMI was increased by frequent milking, but not by suckling, and, in both cases, DMI was insufficient to support the enhanced milk production, and the cows lost BW.

ACKNOWLEDGMENTS

The authors are grateful to U. Lavin and Y. Short and to the staff of the dairy herd of Kibbutz Kefar Menahem, who provided the facilities to house and care for cows and calves.

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34 Wilde. C. J., D. R. Blatchford, C. H. Knight, and M. Peaker. 1989. Metabolic adaptations in goat mammary tissue during long-term incomplete milking. J. Dairy Res. 5617.

35 Wilde, C. I., D. R. Blatchford, and M. Peaker. 1991. Regulation of mouse mammary cell differentiation by extracellular milk proteins. Exp. Physiol. 76:379.

36 Wilde, C. J.. A. J. Henderson, C. H. Knight, D. R. Blatchford. A. Faulkner, and R. J. Vernon. 1987. Effects of long-term thnce-daily milking on mammary enzyme activity, cell population and milk yield. J. Anim. Sci. 64:533. Journal of Dairy Science Vol. 78, No. 12, 1995

Source: Agric. Research Org, Israel
Author: Bar-Peled, Maltz