Comparison between two milk distribution structures in dairy goats milked at different milking frequencies

Small Ruminant Research 114 (2013) 161–166

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Comparison between two milk distribution structures in dairy goats milked at different milking frequencies A. Torres a , N. Castro b , A. Argüello b , J. Capote a,∗ a b

Instituto Canario de Investigaciones Agrarias (ICIA), La Laguna 38200, Tenerife, Spain Department of Animal Science, Universidad de Las Palmas de Gran Canaria, Arucas 35413, Spain

a r t i c l e

i n f o

Article history: Received 6 March 2013 Received in revised form 26 April 2013 Accepted 30 April 2013 Available online 31 May 2013 Keywords: Milk yield Milk partitioning Milking frequency Dairy goat

a b s t r a c t ˜ and Palmera) in mid lactation Twenty-four dairy goats of 3 breeds (Majorera, Tinerfena, (110 ± 7 d in milk) were milked unilaterally at 2 frequencies (once: X1 or twice daily: X2) for 6 wk to evaluate milk yield and milk composition and to compare two milk distribution structures. On the sampling days, milk volumes of each udder halves were recorded and analyzed. Milk partitioning was divided into: cisternal (CM) and alveolar milk (AM); and into: machine milk (MM), machine stripping milk (MSM), and residual milk (RM). In ˜ breeds did not find significant differences in milk yield and milk Majorera and Tinerfena composition due to milking frequency. In contrast, Palmera goats had an increase of 14% in milk yield when they were milked X2 compared with X1, but the protein content was significantly higher in the milk of X1 (3.92%) than X2 (3.72%). Furthermore, the absence of differences in protein daily yield between X1 and X2, suggested that cheese yield could not be maintained. Milking frequency did not affect CM and AM percentages in the studied breeds. Regarding breed factor, Majorera and Palmera had the highest and lowest CM percentages, respectively, both in X1 and X2. On the other hand, MM and MSM percentages did ˜ and Palmera breeds. However, Majorera not differ due to milking frequency in Tinerfena goats had significant differences in MM (77.29 vs. 71.66%) and MSM (12.67 vs. 17.41%) for X1 and X2, respectively. A breed effect was observed on MM and MSM fractions: Major˜ and Palmera goats had higher MSM era goats had higher MM percentages, while Tinerfena percentages. RM fraction was not affected by milking frequency or breed factors. Finally, no significant correlation coefficients were detected when comparing CM and AM with MM, MSM and RM fractions, which indicates that both milk partitioning structures did not seem to be comparable between them, at least in goat udders that have a more horizontal teat insertion. © 2013 Elsevier B.V. All rights reserved.

1. Introduction The mammary glands in ruminants are composed of functionally separate glands (four in cows and two in goats and sheep). Each gland has its own secretory tissue and cisternal cavities, and each gland is drained by

∗ Corresponding author at: ICIA, Apto. de correos 60, La Laguna 38200, Tenerife, Spain. Tel.: +34 922542800; fax: +34 922542898. E-mail addresses: [email protected], [email protected] (J. Capote). 0921-4488/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2013.04.013

a separate teat (Bruckmaier and Blum, 1998). According to Wilde and Knight (1990), the unilateral alteration of milking frequency indicates that milk yield changes are imposed by local intramammary mechanisms and affects only the treated gland. In addition, Wall and McFadden (2008) explained that experimental design that applied single gland milking eliminated variation among animals due to environment, nutrition and genetic factors and exposed each gland to the same systemic factors. Milk is stored in two interconnected anatomical udder compartments that determine the milkability (Salama

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et al., 2004). Cisternal milk (CM) is located in the cisternal compartment consisting of the gland cistern, the teat cisterns and the large ducts; while alveolar milk (AM) is stored within the alveoli and small interlobular ducts (Marnet and McKusick, 2001). Milk partitioning between both compartments varies according to specie, breed, age, lactation stage, parity and milking interval (Salama et al., 2004; Castillo et al., 2008). Partitioning between CM and AM was formerly determined by drainage of cisternal milk, by using a teat cannula (Peaker and Blatchford, 1988), but new techniques include the use of an oxytocin receptor antagonist to block spontaneous milk ejection (Wellnitz et al., 1999). Differing from dairy cows, small ruminants have proportionally larger cisterns which play an important role in the storage of milk between milkings and can greatly affect the removal of milk at the time of milking (Marnet and McKusick, 2001). Furthermore, udder morphology of many goat and sheep breeds is characterized by having a more horizontal teat insertion (Rovai et al., 2008; Torres et al., 2013), a circumstance that implies manual intervention for complete milk removal. Milk collected during milking can be divided into: machine milk (MM) obtained between attaching the line and the final cessation of the milk flow without the operator having to manipulate the udder; and machine stripping milk (MSM) which requires manual intervention to remove milk not obtained by the machine. Moreover, a milk fraction known as residual milk (RM) remains in the mammary tissue and it can only be collected after administration of pharmacological amounts of oxytocin (Bruckmaier and Blum, 1998). The goals of this study were to evaluate the effects of unilateral milking frequency on milk yield, milk composition and milk component yield; and to compare two milk distribution structures in 3 dairy goat breeds milked at 2 frequencies, and whether there are relevant correlations among them to establish a relationship between CM and AM with MM, MSM and RM. 2. Materials and methods The experimental animal procedures were approved by the Ethical Committee of the Universidad de Las Palmas de Gran Canaria (Arucas, Spain). A total of 24 dairy goats in mid lactation (110 ± 7 DIM) of Majorera ˜ (n = 8; 2.3 ± 0.5 L/d; par(n = 8; 2.7 ± 0.4 L/d; parity = 3.4 ± 1.1), Tinerfena ity = 3.1 ± 1.3), and Palmera (n = 8; 1.8 ± 0.4 L/d; parity = 3.1 ± 1.2) breeds from the experimental farm of the Instituto Canario de Investigaciones Agrarias (ICIA, Tenerife, Spain) were used. The animals were fed with commercial concentrate, maize, lucerne, wheat straw and a vitamin–mineral corrector in accordance with the guidelines issued for lactating goats by Institut National de la Recherche Agronomique (INRA, Paris, France; Jarrige, 1990). The milking frequency before the start of the experimental period was once per day. Goats were milked in a double 12-stall parallel milking parlor equipped with recording jars (4 L ±5%) and a low-line milk pipeline. Milking was performed at a vacuum pressure of 42 kPa, a pulsation rate of 90 pulses/min, and a pulsation ratio of 60/40. The milking routine included wiping dirt off teat ends and stripping 2–3 squirts of milk from each teat, machine milking, machine stripping before cluster removal, and teat dipping in an iodine solution (P3-cide plus; Henkel Hygiene, Barcelona, Spain). During a 6-wk period, goats were milked once daily in the left mammary gland (X1; at 07:00 h), whereas the right mammary gland was milked twice daily (X2; at 07:00 and 17:00 h). Before the start of the experimental period, the goats were exposed to 3 wk of adaptation to X2. Milk volumes were measured by using the recording jars in the milking parlor for each udder half. On the sampling days (wk 2, 4, and 6), milk yield was recorded as MM plus MSM once daily for X1, and MM and MSM twice

daily for X2, according to Capote et al. (2008). Fat (4.0%)-corrected milk (FCM) was calculated according to Salama et al. (2003). Milk samples were analyzed immediately after collection to determine milk composition. Fat, protein, lactose and total solids were determined using a MilkoScan 133 analyzer (Foss Electric, Hillerod, Denmark). Milk composition of X2 was calculated by a weighted average from the a.m. and the p.m. milk composition. Milk component yields were calculated by multiplying milk yield by corresponding milk component percentages. Milk partitioning was calculated at the a.m. milking (24- and 14-h milking intervals for X1 and X2, respectively). During wk 1, 3, and 5, on the sampling days, each goat was injected intravenously with 0.8 mg of an oxytocin receptor blocking agent (Tractocile; Ferring, Madrid, Spain) inside a holding pen immediately before entering the milking parlor to record CM volume. After CM removal, the goats were injected intravenously with 2 IU of oxytocin (Oxiton; Laboratorios Ovejero, León, Spain) to reestablish milk ejection, and AM was measured. During wk 2, 4, and 6, on the sampling days, milk partitioning was divided into MM, MSM performed by the same milker, and RM obtained after injecting goats with 2 IU of oxytocin. A MIXED model procedure (SAS 9.0; SAS Institute Inc., Cary, NC) was used. The statistical model included the fixed effects of milking frequency ˜ or Palmera), the random effect (X1 or X2) and breed (Majorera, Tinerfena, of the half-udder nested within animal, the respective interactions, and the residual error: Yijk =  + Bi + Mj + Gk + (BM)ij + εijk where Yijk is the observation of the dependent variable,  is the overall mean, Bi is the effect of the breed i (i = 3), Mj is the effect of the milking frequency j (j = 2), Gk is the random effect, (BM)ij is the effect of the interaction between breed and milking frequency, εijk is the residual error. Differences among the breeds and milking frequencies were evaluated using a multiple comparison test following the Tukey–Kramer method. Pearson’s correlation coefficients between milk fractions were also calculated. Statistical differences were considered significant at P < 0.05. Data are presented as least squares means.

3. Results Milk yield and FCM (Table 1) did not differ due to milk˜ breeds (P > 0.05). ing frequency in Majorera and Tinerfena Nevertheless, Palmera breed had a significant increase in milk yield by 14% when they were milked X2 compared with X1. Furthermore, FCM of X2 was higher than in X1 udder halves by 18% in Palmera goats (P < 0.05). Regarding breed effect, Majorera goats had higher milk yield values than Palmera goats both in X1 and X2 (P < 0.05). No differences were found in fat percentages in the studied breeds (Table 1) when the milking frequency effect was considered (P > 0.05). Besides, Palmera breed had higher ˜ both in X1 and milk fat content than Majorera and Tinerfena X2, but the differences were significant only in X2. Milking frequency did not have effect on the protein percentages in ˜ goats (Table 1). However, Palmera Majorera and Tinerfena goats had higher milk protein content in X1 than in X2 udder halves (P < 0.05). Regarding breed effect, Majorera ˜ had lower protein fraction than Palmera both and Tinerfena in X1 and X2 (P < 0.05). No significant differences were detected in lactose content among breeds and milking frequencies (Table 1), ranging from 4.78 to 4.86% in the studied conditions. Likewise, total solids percentages were not affected due to milking frequency (Table 1) (P > 0.05). Moreover, differences in total solids percentages were found when the breed effect was considered (P < 0.05). Thus, Palmera goats ˜ both in X1 had higher values than Majorera and Tinerfena and X2.

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Table 1 Milk yield, milk composition and milk component yield of each udder half of three dairy goat breeds milked once (X1) or twice (X2) daily.a Parameter

Goat breed

SEM ˜ Tinerfena

Majorera X1

X2

1.39ab 1.34a 3.79b 3.67bc 4.83

Milk yield (L/d) FCMb (L/d) Fat (%) Protein (%) Lactose (%)

Palmera

X1

1.51a 1.50a 3.94b 3.59c 4.86

X2

1.27ab 1.21ab 3.76b 3.63bc 4.85

X1

1.31ab 1.28a 3.88b 3.51c 4.83

X2

1.04c 1.05b 4.06ab 3.92a 4.78

1.19b 1.24a 4.29a 3.72b 4.81

0.049 0.045 0.060 0.041 0.028

Total solids (%)

12.99b

13.06b

12.92b

12.91b

13.58a

13.53a

0.083

Fat (g/d) Protein (g/d) Lactose (g/d)

52.47a 50.95a 67.20ab

59.42a 54.40a 73.65a

46.90ab 44.78ab 61.70ab

50.00ab 44.73ab 64.22ab

41.77b 40.79b 49.96c

50.98a 44.45ab 57.48b

1.785 1.504 2.513

197.58a

162.07ab

180.42a

Total solids (g/d)

168.04a

141.01b

161.42a

5.936

a–c

Means with different superscripts within the same row are different (P < 0.05). a Data are least squares means and standard error of means. b FCM = total milk yield (L/d) × (0.400 + 0.150 × total fat content (%)).

˜ goats were not different in milk Majorera and Tinerfena component yields between X1 and X2 (Table 1). In contrast, Palmera goats had significant increases by 22%, 15%, and 14% in X2 daily yields of fat, lactose and total solids, respectively, compared with X1. However, protein yield did not significantly increase as did the other milk components. CM and AM percentages (Table 2) did not differ due to milking frequency in the studied breeds (P > 0.05). Majorera and Palmera had the highest and lowest CM percentages, respectively, both in X1 and X2 (P < 0.05). In the same way, MM and MSM percentages (Table 2) were not affected ˜ and Palmera breeds by milking frequency in Tinerfena (P > 0.05). However, Majorera goats had higher and lower values in MM and MSM fractions, respectively, in X1 with regard to X2. RM percentages were not affected by the milking frequency and breed factors (P > 0.05), ranging from 10.66 to 14.49% in the studied conditions. Correlation coefficients among milk fractions are reported in Table 3. High negative correlations between MM and MSM fractions (P < 0.05) were observed for ˜ X1 (Majorera, r = −0.76; Tinerfena, r = −0.94; Palmera, ˜ r = −0.70; r = −0.90) and X2 (Majorera, r = −0.72; Tinerfena, Palmera, r = −0.90). Moreover, MM and RM were only sig˜ nificantly correlated for X1 (Majorera, r = −0.82; Tinerfena,

r = −0.93; Palmera, r = −0.86). In addition, no significant correlation coefficients were found between MSM and RM for X1 and X2. Finally, CM and AM were not correlated with MM, MSM and RM fractions in the studied breeds milked at X1 and X2 (P > 0.05).

4. Discussion The increase in milk yield in Palmera goats was higher ˜ goats (6%) by Capote than the values reported in Tinerfena et al. (1999) and Damascus goats (7%) by Papachristoforou et al. (1982) and similar to loss caused by X1 in Alpine goats (16%) by Komara et al. (2009). The increase in FCM in Palmera goats was comparable with the FCM value reported in Murciano-Granadina goats (18%) by Salama et al. (2003). However, the goats of those studies were milked with the same frequency in both glands. The unilateral milking frequency effect indicates that the increase in milk yield is a response strictly at the level of the mammary gland via local factors, and not due to the greater availability of nutrient supply caused by the suppression of milking in the opposite gland (Nudda et al., 2002; Wall and McFadden, 2008).

Table 2 Milk fractions of three dairy goat breeds milked once (X1) or twice (X2) daily.a,b Fractionc

Goat breed

SEM ˜ Tinerfena

Majorera

CM (%) AM (%) MM (%) MSM (%) RM (%) a–c

Palmera

X1

X2

X1

X2

X1

X2

82.28a 18.41c 77.29a 12.67c 10.66

81.75a 18.77c 71.66b 17.41b 11.61

80.12ab 20.15bc 67.21bc 19.71b 12.96

80.30ab 19.99bc 61.21c 24.94ab 14.49

77.22bc 23.02ab 65.86bc 22.34ab 12.48

76.70c 23.43a 59.07c 27.57a 13.24

Means with different superscripts within the same row are different (P < 0.05). Data are least square means and standard error of means. b Milk fractions were measured at 24- and 14-h milking intervals for X1 and X2 goats, respectively. c CM, cisternal milk; AM, alveolar milk; MM, machine milk; MSM, machine stripping milk; RM, residual milk. a

0.528 0.498 1.366 1.100 0.449

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Table 3 Pearson’s correlation coefficients matrix among milk fractions of three dairy goat breeds milked once (above diagonal) or twice (below diagonal) daily. Breed

Fractiona CM

AM

MM

MSM

RM

−0.885* −0.989* −0.987*

−0.285 0.084 −0.051

0.379 −0.050 0.162

0.181 −0.159 0.007

−0.007 −0.189 0.008

−0.245 0.143 −0.136

0.173 0.232 0.023

−0.761* −0.941* −0.897*

−0.823* −0.933* −0.863*

CM

Majorera ˜ Tinerfena Palmera

AM

Majorera ˜ Tinerfena Palmera

−0.892* −0.935* −0.990*

MM

Majorera ˜ Tinerfena Palmera

0.411 0.067 0.617

−0.550 −0.082 −0.586

MSM

Majorera ˜ Tinerfena Palmera

−0.164 0.158 −0.615

0.314 −0.210 0.636

−0.721* −0.702* −0.895*

RM

Majorera ˜ Tinerfena Palmera

0.128 −0.476 0.024

0.053 0.433 −0.107

−0.050 −0.253 −0.406

* a

0.139 0.694 0.666 −0.258 −0.107 0.006

P < 0.05. CM, cisternal milk; AM, alveolar milk; MM, machine milk; MSM, machine stripping milk; RM, residual milk.

The differences observed in milk yield in Majorera, Tin˜ and Palmera goats between X1 and X2 may be erfena explained as a consequence of cisternal capacity of each breed (Bruckmaier and Blum, 1998). A large voluminous cistern takes more time in filling up, delaying the effects of the intramammary feedback inhibitor, intramammary pressure, or tight junction integrity on milk transference from the alveoli to the cisterns, during the filling of the udder (Capote et al., 2008). Recently, serotonin has been proposed as a feedback inhibitor of lactation, being a component involved in milk regulation (Hernandez et al., 2008). However, milk yields did not differ between treatment and control halves, which suggest that serotonin is not a local factor. In addition, Silanikove et al. (2000) showed in goats and cows that the plasmin-induced ␤-casein f(1–28) peptide can serve as a local regulator on milk secretion by functioning as a potassium channel blocker, which was subsequently confirmed in dairy cows by Silanikove et al. (2009). It is predicted that for milking intervals of less than 20 h in goats and 18 h in cows, the concentration of caseinderived peptides, including the active component ␤-casein f(1–28), would be higher in the cistern than in the alveoli; therefore, the alveoli will not be exposed to the full impact of the negative feedback signal of this peptide. Extending milk stasis beyond these times exceeds the storage capacity of the cistern, resulting in the equilibration of ␤-casein f(1–28) concentration between the cistern and the alveoli (Silanikove et al., 2010). Thus, animals with smaller udder size, and hence of cisternal compartment, such as Palmera goats (SuárezTrujillo et al., 2013; Torres et al., 2013), are more affected by mechanisms of feedback inhibition. Silanikove et al. (2010) explained that high milk producing goats, as Saanen, selected to high alveolar to cistern compartment ratio, are the most sensitive to changes in milking frequency. In contrast, medium milk producing goats, as some Spanish breeds, may attain their genetic potential for milk yield in

X1 regimen due to selection for high cistern capacity. The physiological explanation relates to the suggestion that ␤casein f(1–28) is effective only in the alveoli where it is in contact with the epithelial cells. Exposing the alveoli to high concentration of ␤-casein f(1–28) will induce disruption of the tight junction (Silanikove et al., 2010). Milk fat content was not affected by milking frequency which is in accordance with Komara et al. (2009), who also did not observe differences in fat globule size between X1 and X2 for Alpine goats. However, Salama et al. (2003) showed that milk of X1 goats had a 10% more fat content than milk of X2 goats. Milk fat is considered to be the most variable component in ruminant milk, due to differing regulatory mechanisms for secretion of milk fat globules relative to the components in the aqueous phase of milk and to the transfer between alveolar and cisternal compartments (Salama et al., 2003). X1 management in high-yielding goats is a potent stressor that is able to disturb alveolar milk ejection because alveolar milk was shown to contain up to 75% of milk fat when milk ejection was inhibited (Labussière, 1988). However, the absence of significant differences in the studied breeds might be due to the fact that approximately 80% of total milk was stored in the cisternal compartment and most of the transfer of milk fat from the alveoli to the cistern had already taken place. Milk protein concentration was significantly higher in X1 than in X2 udder halves in Palmera goats, which agrees with observations in dairy goats by Komara et al. (2009) and dairy ewes by Nudda et al. (2002). Salama et al. (2003) explained that the concentration effect of the protein in X1 with respect to X2 was due to the milk volume, this was lower with X1 but the casein synthesized remained and became more concentrated in the milk. In goats, Capote et al. (1999) found that milking frequency did not affect lactose percentage and reiterate the assertion that lactose is the milk component least influenced by breed and milking factors, indicating a similar

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performance of the synthetic activity of the mammary gland. In the studied breeds there were no significant differences found in total solids content between X1 and X2. There is disagreement about the milking frequency effects on total solids percentages. Capote et al. (1999) had observed a lower total solids fraction in X1 (12.48%) than X2 (12.84%), while for Salama et al. (2003) the total solids were higher in X1 (13.60%) than X2 (12.90%) in goats during an entire lactation. Finally, the fact that Palmera goats had higher percentages of ˜ both in X1 total solids than Majorera and Tinerfena and X2, may be explained because the Palmera had higher percentages of fat and protein than the other two breeds. The increases in fat, lactose, and total solids yields were consistent with the significant increase in the milk production of Palmera goats. However, the absence of differences in protein yield between X1 and X2 can be explained by a lower concentration of protein in X2, suggesting that cheese yield could not be maintained. Marnet and Komara (2008) explained that the regulation of milk components synthesis is dependent on the duration of the milking interval, which can influence cheese-making capacity and cheese quality. Despite the differences in milk yield in Palmera goats between X1 and X2, there were not differences in the distribution of milk in the udder. Salama et al. (2004) did not find differences in milk accumulation rates in the cisternal compartment at 16 and 24 h in Murciano-Granadina goats milked X1 or X2, whereas Torres et al. (2013) suggested that the high percentages of milk stored in cisternal compartments for 14- and 24-h milking intervals may be explained by a greater transfer of milk from the alveoli to the cisterns during early udder filling. The differences in milk partitioning among breeds were due to the cisternal size of each breed that influences the capacity to store milk in this compartment. For example, Rovai et al. (2008) found CM–AM ratio of 59–41 and 77–23 for Manchega and Lacaune ewes, respectively, where Lacaune breed presented a greater cisternal area than Manchega breed (24.0 vs. 12.4 cm2 ). MM and MSM percentages were higher and lower, respectively, in X1 udder halves in the studied breeds, but the differences were significant only in Majorera goats. Previously, Capote et al. (2009) found no differences in MM percentages between X1 (67.8%) and X2 (64.5%) in ˜ goats of high milk production, while MSM perTinerfena centages were higher in X2 (27.8%) than X1 (20.7%), and RM percentages were higher in X1 (11.5%) than X2 (7.7%), suggesting that an increase in milking frequency in a normal routine implies greater stimulation and thus a higher milk drop to the cisterns. Moreover, Majorera goats had a higher and lower MM and MSM percentages, respec˜ and Palmera goats. Caja et al. (1999) tively, than Tinerfena explained that quantities of milk in each partition obtained by mechanical milking depend on the udder morphology and the development of cisternal and canalicular systems; which suggests a high variability between breeds and even between animals of same breed. RM percentages were not affected by the breed, and they were similar than those

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reported in Murciano-Granadina (9–11%; Peris et al., 1996) ˜ (7–12%; Capote et al., 2009) goats. and Tinerfena In addition, Marnet and McKusick (2001) reported significant increases in MSM percentage without proportional modification of AM or CM volume in Lacaune ewes between the years 1982 and 1992. The increase in MSM fraction was a consequence of the tendency to have more horizontally placed teats in the udder which increases cisternal storage capacity to improve milk production (Bruckmaier et al., 1997; Marnet and McKusick, 2001). High negative correlations observed between MM and MSM fractions both in X1 and X2 in the studied breeds differs with these observed by Peris et al. (1996) and Caja et al. (1999) who did not find significant correlations between both fractions. However, it is clear that the correlation between both them could help in the selection of goats to improve the milkability. Furthermore, Peris et al. (1996) noted that the negative correlation between MM and RM in goats could reduce the milking time because they accumulate more milk into the cisterns. Although, CM and AM (Salama et al., 2004) or MM, MSM and RM percentages (Capote et al., 2008) have a strong dependence on udder morphology, the absence of significant correlation coefficients between CM and AM with MM, MSM, and RM fractions impeded the establishment of a relationship between both milk partitioning structures, at least in goat udders that have a more horizontal teat insertion. 5. Conclusion The results demonstrated that X2 practice did not improve the milk production of the Majorera and Tin˜ breeds, so it is a consequence of the adaptation erfena of these breeds to X1, which is an interesting issue in goat production systems, because it requires fewer variable costs. Nevertheless, the high increase in milk yield in the Palmera goats due to X2 could seem a profitable management at certain times during the lactation. However, this practice did not produce an increased in milk protein yield in accordance with milk yield. Therefore, other studies are required to evaluate how the milking frequency affects the cheese yield, which is a very important part of the Canary Islands livestock economy. Additionally, the knowledge of the structures of milk partitioning can serve as a basis for future selection programs to improve the milkability of the studied breeds. Furthermore, if a wider selection of breeds could be studied, ranging from low milk yielding to high milk yielding breeds, the relationship among milk fractions would be more noticeable. Conflict of interest None. Acknowledgment This work was supported by Fondo Europeo de Desarrollo Regional-Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (FEDER-INIA) RTA200900125.

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References Bruckmaier, R.M., Paul, G., Mayer, H., Schams, D., 1997. Machine milking of Ostfriesian and Lacaune dairy sheep: udder anatomy, milk ejection and milking characteristics. J. Dairy Res. 64, 163–172. Bruckmaier, R.M., Blum, J.W., 1998. Oxytocin release and milk removal in ruminants. J. Dairy Sci. 81, 939–949. Caja, G., Capote, J., López, J.L., Peris, S., Such, X., Argüello, A., 1999. Milk partitioning and milk flow rate of Canarian dairy goats under once daily or twice daily milking frequencies. In: Barillet, F., Zervas, N.P. (Eds.), Milking and Milk Production of Dairy Sheep and Goats. Wageningen Pers, Wageningen, pp. 274–280. Capote, J., López, J.L., Caja, G., Peris, S., Argüello, A., Darmanin, N., 1999. The effects of milking once or twice daily throughout lactation on milk production of Canarian dairy goats. In: Barillet, F., Zervas, N.P. (Eds.), Milking and Milk Production of Dairy Sheep and Goats. Wageningen Pers, Wageningen, pp. 267–273. Capote, J., Castro, N., Caja, G., Fernández, G., Briggs, H., Argüello, A., 2008. Effects of the frequency of milking and lactation stage on milk fractions ˜ dairy goats. Small Rumin. Res. 75, and milk composition in Tinerfena 252–255. Capote, J., Castro, N., Caja, G., Fernández, G., Morales-delaNuez, A., Argüello, A., 2009. The effects of the milking frequency and milk ˜ dairy goats. Milchproduction levels on milk partitioning in Tinerfena wissenschaft 64, 239–241. Castillo, V., Such, X., Caja, G., Salama, A.A.K., Albanell, E., Casals, R., 2008. Changes in alveolar and cisternal compartments induced by milking interval in the udder of dairy ewes. J. Dairy Sci. 91, 3403–3411. Hernandez, L.L., Stiening, C.M., Wheelock, J.B., Baumgard, L.H., Parkhurst, A.M., Collier, R.J., 2008. Evaluation of serotonin as a feedback inhibitor of lactation in the bovine. J. Dairy Sci. 91, 1834–1844. Jarrige, J., 1990. Alimentación de bovinos, ovinos y caprinos (Nutrition in bovine, ovine and caprine), first ed. Mundi Prensa, Madrid, Spain. Komara, M., Boutinaud, M., Ben Chedly, H., Guinard-Flament, J., Marnet, P.G., 2009. Once-daily milking effects in high-yielding alpine dairy goats. J. Dairy Sci. 92, 5447–5455. Labussière, J., 1988. Review of the physiological and anatomical factors influencing the milking ability of ewes and the organization of milking. Livest. Prod. Sci. 18, 253–274. Marnet, P.G., Komara, M., 2008. Management systems with extended milking intervals in ruminants: regulation of production and quality of milk. J. Anim. Sci. 86, 47–56. Marnet, P.G., McKusick, B.C., 2001. Regulation of milk ejection and milkability in small ruminants. Livest. Prod. Sci. 70, 125–133.

Nudda, A., Bencini, R., Mijatovic, S., Pulina, G., 2002. The yield and composition of milk in Sarda, Awassi, and Merino sheep milked unilaterally at different frequencies. J. Dairy Sci. 85, 2879–2884. Papachristoforou, C., Roushias, A., Mavrogenis, A.P., 1982. The effect of milking frequency on the milk production of Chios ewes and Damascus goats. Ann. Zootech. 31, 37–46. Peaker, M., Blatchford, D.R., 1988. Distribution of milk in the goat mammary gland and its relation to the rate and control of milk secretion. J. Dairy Res. 55, 41–48. Peris, S., Such, X., Caja, G., 1996. Milkability of Murciano-Granadina dairy goats. Milk partitioning and flow rate during machine milking according to parity, prolificacy and mode of suckling. J. Dairy Res. 63, 1–9. Rovai, M., Caja, G., Such, X., 2008. Evaluation of udder cisterns and effects on milk yield of dairy ewes. J. Dairy Sci. 91, 4622–4629. Salama, A.A.K., Such, X., Caja, G., Rovai, M., Casals, R., Albanell, E., Marín, M.P., Martí, A., 2003. Effects of once versus twice daily milking throughout lactation on milk yield and milk composition in dairy goats. J. Dairy Sci. 86, 1673–1680. Salama, A.A.K., Caja, G., Such, X., Peris, S., Sorensen, A., Knight, C.H., 2004. Changes in cisternal udder compartment induced by milking interval in dairy goats milked once or twice daily. J. Dairy Sci. 87, 1181–1187. Silanikove, N., Shamay, A., Shinder, D., Moran, A., 2000. Stress down regulates milk yield in cows by plasmin induced ␤-casein product that blocks K+ channels on the apical membranes. Life Sci. 67, 2201–2212. Silanikove, N., Shapiro, F., Shinder, D., 2009. Acute heat stress brings down milk secretion in dairy cows by up-regulating the activity of the milkborne negative feedback regulatory system. BMC Physiol. 9, 13. Silanikove, N., Leitner, G., Merin, U., Prosser, C., 2010. Recent advances in exploiting goat’s milk: quality, safety and production aspects. Small Rumin. Res. 89, 110–124. Suárez-Trujillo, A., Capote, J., Argüello, A., Castro, N., Morales-delaNuez, A., Torres, A., Morales, J., Rivero, M., 2013. Effects of breed and milking frequency on udder histological structures in dairy goats. J. Appl. Anim. Res. 41, 166–172. Torres, A., Castro, N., Hernández-Castellano, L.E., Argüello, A., Capote, J., 2013. Effects of milking frequency on udder morphology, milk partitioning, and milk quality in 3 dairy goat breeds. J. Dairy Sci. 96, 1071–1074. Wall, E.H., McFadden, T.B., 2008. Use it or lose it: enhancing milk production efficiency by frequent milking of dairy cows. J. Anim. Sci. 86, 27–36. Wellnitz, O., Bruckmaier, R.M., Albrecht, C., Blum, J.W., 1999. Atosiban, an oxytocin receptor blocking agent: pharmacokinetics and inhibition of milk ejection in dairy cows. J. Dairy Res. 66, 1–8. Wilde, C.J., Knight, C.H., 1990. Milk yield and mammary function in goats during and after once-daily milking. J. Dairy Res. 57, 441–447.