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* Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
Facultad de Agronomía, Universidad Autònoma de San Luis Potosí, 78321 San Luis Potosí, México
Sheep and Goat Research Department, Animal Production Research Institute, 4 Nadi El-Said St., 12311 Dokki, Giza, Egypt
1 Corresponding author: gerardo.caja{at}uab.es
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: lactation induction • somatotropin • milk composition • dairy ewes
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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To improve the response of cows, ewes, and goats to the induction treatment, researchers have added placental lactogen (Byatt et al., 1997; Kann et al., 1999), somatotropin (Kann, 1997; Kann et al., 1999; Kensinger et al., 2006), prostaglandins (Lukas et al., 2003), reserpine (Collier et al., 1977; Kensinger et al., 1979; Salama et al., 2007), and thyroid hormones (Hart and Morant, 1980; Head et al., 1980). The effects reported by using reserpine, a prolactin releaser, suggest that differences in the response to lactation induction occur because of season of the year and the photoperiod sensitivity of the animals.
Most studies of lactation induction in sheep have been conducted with Prealpes du Sud ewes (Kann, 1997; Kann et al., 1999; Head et al., 1980), which is a dual-purpose local French breed and not a true dairy sheep, or with local dairy ewes of a nonspecified breed (Alifakiotis et al., 1980). Kann (1997) and Kann et al. (1999) concluded that the inclusion of growth hormone in the induction protocol is necessary to improve milk yield in ewes.
To our knowledge, no studies have been conducted to evaluate the results of induced lactation in specified dairy sheep breeds in which a greater success rate and milk yield should be expected. Moreover, little is known about differences in milk composition in dairy ewes that have been artificially or naturally induced to lactate.
The aim of this study was to compare the lactational response to hormonal treatment of lactation induction in ewes of 2 dairy breeds that differ in their productive potential. Induced lactation by the standard protocol proposed by Smith and Schanbacher (1973) was compared with natural lactation during winter (experiment 1), and this standard protocol was compared with a modified protocol with bST in spring (experiment 2).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Animals and Treatments
Experiment 1.
A total of 46 ewes from 2 dairy breeds that differed in milk production potential (Manchega, medium yield, n = 28; Lacaune, high yield, n = 18) were used to study the response to lactation induction by a standard protocol based on the use of steroid hormones. During winter, 23 dairy ewes were artificially (ART) induced into lactation (Manchega, n = 14; 9 nulliparous and 5 multiparous; and Lacaune, n = 9; 4 nulliparous and 5 multiparous) and compared with 23 dairy ewes naturally (NAT) lambed (Manchega, n = 14; 9 primiparous and 5 multiparous; and Lacaune, n = 9; 5 primiparous and 4 multiparous) at the experimental farm of the S1GCE de la Universitat Autonoma de Barcelona in Bellaterra, Spain (41°30' N, 2°5' E).
To eliminate the possible effect of the reproductive state of the ewes on the response to hormones used to induce lactation, ART ewes were estrus synchronized (starting January 23) for 12 d by insertion of a polyurethane vaginal sponge that contained 40 mg of fluorogestone acetate (Chronolone, Intervet, Salamanca, Spain), and 400 IU of pregnant mare serum gonadotropin (Foligon, Intervet) i.m. was injected at the time of sponge withdrawal. Five days after sponge withdrawal, ewes were induced into lactation by using the standard protocol of Smith and Schanbacher (1973) based on daily s.c. injections of estradiol-17β (0.5 mg/kg of BW) and progesterone (1.25 mg/kg of BW) in 2 portions at 0800 and 1800 h from d 1 to 7. Lactation was triggered by hydrocortisone acetate (50 mg/d) injected s.c. daily for 3 d (d 18 to 20). Milking was initiated on d 21 (February 28) and was continued for 13 wk.
The NAT groups of ewes naturally lambed from each breed for use in the contemporary comparison of NAT vs. ART lactation were selected from the dairy flock of the S1GCE (Servei de Granges i Camps Experimentals) according to lambing dates. The NAT ewes were mated after synchronization by ram effect, lambed on February 22 (±5 d), and suckled their lambs for 4 wk. Milking was initiated after weaning the lambs at 27 d of age (March 21) and was continued for 154 d (22 wk). Animals and treatments used in experiment 1 are summarized in Table 1
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Manchega ewes (n = 19) were divided into 2 groups in early spring, estrus-synchronized via vaginal sponges (starting April 10), and induced into lactation by the same standard protocol used in experiment 1 or by the same protocol in which bST was included. Ewes of the standard protocol were used as a control (control: 6 nulliparous and 3 multiparous). Ewes of the modified protocol were injected s.c. with a single dose of prolonged-release bST (Lactotropina, 250 mg/ewe; Elanco Animal Health Mexico, Guadalajara, Jalisco, México) on d 11 (bST: 7 nulliparous and 3 multiparous). The animals and treatments used in experiment 2 are also summarized in Table 1
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Hormones
Steroid hormones for lactation induction were supplied by Sigma-Aldrich (Sigma-Aldrich Química, Barcelona, Spain). Estradiol-17β, progesterone, and hydrocortisone acetate were dissolved in dimethyl sulfoxide (USP grade DMSO, Gaylord Chemical Co., Slidell, LA) to give concentrations of 1,003, 44, and 245 g/L, respectively. Solutions were protected from light and stored at room temperature. Insulin syringes (1 mL, BD Medical-Diabetes Care, San Agustín del Guadalix, Madrid, Spain) were used for estradiol and hydrocortisone acetate injections.
The bST (Lactotropina) was supplied by Elanco Animal Health Mexico as syringes of 500 mg of zinc bovine somatotropin and stored at 4°C until their use. Each bST syringe was measured and carefully marked to use one half for each ewe (250 mg/ewe).
Feeding and Management Conditions
Ewes grazed for 6 h daily on an Italian ryegrass pasture and were fed indoors with dehydrated Italian rye-grass hay ad libitum (12% CP; as fed) and 0.5 kg of alfalfa pellets (17% CP; as fed). Ewes were milked twice daily (0800 and 1700 h) in a double-12 stall parallel milking parlor (Westfalia-Separator Ibérica, Granollers, Spain) provided with individual feeders, headlocks, recording jars (2 L ± 5%), and a low milk pipeline. A total of 0.6 kg/d of commercial concentrate (6.4 MJ of NEL/kg and 16% CP; as fed) was distributed in 2 portions at the a.m. and p.m. milkings.
The milking machine was set at a vacuum pressure of 42 kPa, a pulsation rate of 120 pulses/min, and a pulsation ratio of 50%. The milking routine included machine milking, stripping before cluster removal, and teat dipping in an iodine solution (P3-cide plus, Henkel Hygiene, Barcelona, Spain).
Sample Collection, Analyses, and Measurements
Milk yield in the lactation-induced ewes was recorded daily during the first week of lactation and thereafter weekly until wk 13 (experiment 1) or wk 5 (experiment 2) of lactation. No data were available for NAT ewes from wk 1 to 4 in experiment 1 because they were suckling their lambs. Consequently, the comparison between NAT and ART ewes in experiment 1 was based on data collected from wk 5 to 13.
Milk composition was evaluated daily during wk 1 (experiment 1) and biweekly through wk 13 (experiment 1) and wk 5 (experiment 2). Milk samples of approximately 100 mL were collected individually and preserved with an antimicrobial tablet (Bronopol, Broad Spectrum Microtabs II, D&F Control Systems, San Ramon, CA) at 4°C until analysis. Unhomogenized milk samples were analyzed with a near-infrared spectrometer (Foss NIR-Systems 5000, Foss, Hillerød, Denmark) for content of TS, fat, protein (N x 6.38), true protein, and CN (Albanell et al., 1999). Whey protein was calculated by the difference between true protein and CN, and NPN was calculated by the difference between protein and true protein.
Statistical Analyses
Data were analyzed by the MIXED procedure for repeated measurements of SAS (SAS 9.1; SAS Inst. Inc., Cary, NC). The statistical mixed model contained the random effect of the animal within the treatment (NAT vs. ART in experiment 1; control vs. bST in experiment 2); the fixed effects of treatment, parity, and week of lactation; the interaction between treatment and week of lactation, and between treatment and parity; and the residual error. For experiment 2, a group effect (ewes previously induced in experiment 1 vs. ewes induced for the first time in experiment 2) was added to the model. Differences were detected by the PDIF test and significance was declared at P < 0.05 unless otherwise indicated.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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As a consequence of the high level of estrogens used, ewes showed signs of prolonged estrus behavior during the 2 wk after the induction treatment while udders began to fill with mammary secretions. Similar behavior has been observed in cows (Smith and Schanbacher, 1973) and goats (Salama et al., 2007).
Experiment 1
Milk Yield.
Response to the lactation induction treatment during winter differed between Manchega and Lacaune ewes. Most Manchega ewes (79%) failed to be induced into lactation (of 14 ewes, only 2 nulliparous and 1 multiparous ewe produced more than 200 mL/d in wk 2 of milking) with the standard protocol used, whereas all Lacaune ewes were successfully induced to lactate (all ewes produced more than 400 mL/d at wk 2). A daily milk yield of 200 mL was taken as a criterion for lactation induction success according to the International Committee for Animal Recording (2005) minimum standard quantity of milk for milk recording in dairy sheep. To our knowledge, this is the first study showing a marked difference in the response to lactation induction based on genetic differences.
Lacaune dairy ewes yield more milk than Manchega ewes under the same management conditions (Molina et al., 2001; Marie et al., 2002), which implies that a different physiological milieu exists in each breed. Cows of high genetic merit produced more milk and had greater concentrations of plasma growth hormone than cows of low genetic merit (Kazmer et al., 1986; Westwood et al., 2000). Previous studies in Prealpes du Sud ewes, a low-milk-yielding breed, showed that the inclusion of growth hormone in the induction protocol improved the success rate and milk yield (Kann et al., 1999). Fernández et al. (1995) showed a 34 to 53% increase in milk yield of Manchega dairy ewes treated with bST, in the range of 80 to 240 mg/ewe during lactation. Hormone levels, hormone receptors, transcription factors, or other factors that are involved in seasonal productive processes in the Lacaune ewes might have allowed them to respond better to the induction treatment; consequently the need for growth hormone in the induction protocol might be greater in Manchega than in Lacaune ewes. We cannot rule out the possibility that if Lacaune ewes had been treated with bST during the induction treatment, they would have yielded more milk.
In this experiment, ART Manchega ewes were dried off and a lactational performance comparison between NAT and ART was possible only for Lacaune ewes (Figure 1). At all weeks, differences in milk yield between NAT and ART Lacaune ewes were significant (P < 0.001) and, on average (wk 5 to 13), ART ewes yielded 49% the quantity of milk produced by NAT ewes (1.23 ± 0.14 vs. 2.51 ± 0.15 L/d; P < 0.001). This percentage fell within the range of 25 to 50% reported by Head et al. (1980) in Prealpes du Sud ewes and showed that lactation induction was only partly satisfactory.
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There were no differences in milk yield between nulliparous (1.04 ± 0.19 L/d) and multiparous (1.00 ± 0.21 L/ d) Lacaune ewes in the ART group. Nevertheless, multiparous NAT ewes produced more milk than primiparous NAT ewes (2.95 ± 0.21 vs. 2.08 ± 0.18 L/d; P < 0.01). One may expect a greater response to induced lactation in multiparous than in nulliparous ewes, because multiparous ewes should have had more secretory cells exposed to the hormonal treatment. However, it seems that the induction treatment resulted in the activation of a similar number of cells regardless of parity number in ART ewes. On the other hand, consecutive pregnancies in multiparous animals resulted in a higher number of activated mammary secretory cells than in primiparous animals that lambed once.
Milk Composition.
Milk composition on the first day of induced lactation (d 21) in ART Lacaune ewes averaged TS, 16.5%; fat, 4.02%; protein (data not shown), 8.52%; CN, 3.85%; whey protein, 4.66%; and NPN, 0.48%. Milk composition changed dramatically during the first week of lactation in ART ewes, as shown in Figure 2.
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Milk protein and CN percentages in ART Lacaune ewes were high during the first 2 d of lactation, decreased by d 3 (P < 0.05) to standard milk values, and remained constant thereafter (Figure 2). Similar changes were reported in induced nulliparous dairy goats (Salama et al., 2007). On the other hand, milk fat and TS values stabilized later than milk protein and CN, and from d 7 onward these values were constant (Figure 2).
Despite the large and significant difference between NAT and ART Lacaune ewes in milk yield, there were no differences in milk composition from wk 5 to 13 (Table 2 and Figure 2), except that whey protein was greater in ART than in NAT ewes. Similarly, the composition of milk from induced lactation was not different from milk from lactations that followed parturition in dairy cows (Narendran et al., 1974) and dairy goats (Chilliard et al., 1986). The lack of differences between groups in the main milk components suggested that the induction treatment resulted in less mammary cell hyperplasia than did pregnancy-initiated lactation; however, the bio-synthetic capacity of the cells was similar.
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). Salama et al. (2007) also reported that milk of goats induced to lactate contained a lower CN:protein ratio than milk of normally lactating goats. The low CN:protein ratio in NAT ewes may be a consequence of the negative energy balance observed during early lactation in Lacaune ewes under similar feeding conditions (Molina et al., 2001; Marie et al., 2002).
Experiment 2
Milk Yield.
The Manchega ewes that responded poorly to the standard protocol in experiment 1 during winter (success rate, 21%) responded much better in experiment 2, which was conducted during spring. Milk yields in the first 2 wk of lactation were greater than 200 mL/d for 14 of 19 ewes (success rate, 74%). The success rate of lactation induction did not differ (P = 0.510) between control (67%, 6 of 9 ewes) and bST-treated (80%, 8 of 10 ewes) ewes, or between nulli- and multiparous ewes, although the nulliparous ewes had a higher numerical success rate (69 vs. 33%, respectively; P = 0.111). This result might indicate a different response to the same hormone dose, depending on parity of the ewe. Bridges and Byrnes (2006) reported that previous reproductive experience reduces circulating 17β-estradiol and prolactin levels in rats, and affects the estrogen-mediated processes beyond first lactation. Nulliparous rats were more sensitive than multiparous rats to lower doses of estradiol benzoate, whereas multiparous rats were more responsive to the higher doses.
The increased success rate of lactation induction in experiment 2 might be a consequence of an improvement in the hormonal milieu in Manchega dairy ewes during spring. Lactation induction for experiment 2 was conducted in April, under increasing photoperiod conditions after the spring equinox, whereas the induction in experiment 1 was in January, close to the winter solstice. Kensinger et al. (1979) showed that dairy cows induced into lactation in spring had greater basal levels of prolactin and milk yields than those induced in winter. Moreover, Kann (1997) reported that ewes exposed to a long-day photoperiod had greater plasma concentrations of prolactin, growth hormone, and IGF-I, which may result in a hormonal milieu during spring that promotes greater mammogenesis and lactogenesis. The importance of prolactin for mammogenesis was shown by Salama et al. (2007), who reported that goats treated with reserpine (used as a prolactin releaser around the spring equinox) produced 28% more milk yield than goats induced to lactate without reserpine.
Despite the improved success rate, response to lactation induction in Manchega ewes during spring was still considered unsatisfactory. When the criterion for lactation induction success was increased to milk yield >500 mL/d, success rates were 11 and 60% in control and bST-treated ewes, respectively (P < 0.05).
Milk yield after lactation induction was 98% greater in bST-treated ewes than in control ewes (402 ± 85 vs. 203 ± 86 mL/d; P = 0.096; Figure 3). The difference between groups might have been greater if ewes had been induced under short-day photoperiod conditions. Kann (1997) reported that milk yield enhancements caused by the use of human growth hormone-releasing factor in a lactation induction protocol in ewes were 31 and 148% during long- and short-day photoperiods, respectively. The obtained results suggest an important role for prolactin and bST in the response to lactation induction in dairy sheep.
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) than in experiment 1 (wk 8; Figure 1) or than reported in the literature (wk 8 to 11). Peak milk yield values for control and bST-treated ewes (Figure 3) were only 21 and 32% of the peak values observed in contemporary Manchega ewes lactating naturally after lambing in the same herd (Figure 1). This may be the result of an interrupted or incomplete proliferation or differentiation of the secretory mammary epithelial cells in lactation-induced ewes. The milk yield decrease in control ewes after wk 2 (Figure 3) was unexpected. The use of bST after the start of lactation induction, as reported by Magliaro et al. (2004) in cows, might be a solution to maintain and increase milk yield in Manchega ewes induced to lactate. The milk yield and milk composition response of Manchega dairy ewes to bST doses was evaluated by Fernández et al. (1995).
Milk Composition.
Despite the differences in milk yield discussed previously, milk composition of Manchega ewes induced to lactate was similar in control and bST-treated ewes throughout the experimental period (Table 3). When bST was injected during an established lactation in dairy ewes, milk yield increased, but milk composition was not affected (D’Urso et al., 1998). However, the treatment of Manchega dairy ewes with bST during early and midlactation reduced milk protein in both stages, whereas milk fat increased during early lactation but was not affected during late lactation (Fernandez et al., 1995). Values of milk composition fell within the range reported for normal milk composition after lambing in Manchega dairy ewes (Casals et al., 1999; Molina et al., 2001).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication September 13, 2007. Accepted for publication February 14, 2008.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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, n = 14) dairy ewes milked after the weaning of their lambs and in Lacaune (
, n = 9) dairy ewes artificially induced to lactate (experiment 1).
, n = 10) or without (