Boujenane Iranian Journal of Applied Animal Science (2019) 9(1), 25-29 25 Effects of Milking Frequency on Milk Production and Composition of Holstein Cows during Their First Three Lactations INTRODUCTION The increase of milk production costs and the stabilization of milk prices during the last two decades in Morocco forced the dairy farmers to look for efficient management practices for improving their income. Thus, besides the improvements in feeding, genetics, reproduction, health care and housing, increasing milking frequency, from two to three times daily, has been used as an effective tool of increasing milk production. Effect of milking frequency on milk yield has been studied by several researchers around the world, and numerous reports showed that milking cows three times daily increased production by an average of about 15% relative to milking cows twice daily (Amos et al. 1985; Barnes et al. 1990; Atashi, 2015). The primary causes of this increase are reduction of intra-mammary pressure and proliferation of mammary gland cells from more frequent milk removal (Czerniawska-Piatkowska et al. 2012). Moreover, cows milked three times daily have shown significantly decreased milk fat percentage com- pared with those milked two times daily (Szuchs et al. 1986; Sapru et al. 1997; Smith et al. 2002), however, milk fat yield (Barnes et al. 1990) and protein percentage (Szuchs et al. 1986) were unaffected. Further, some studies (Amos et al. 1985; Barnes et al. 1990; Atashi, 2015) dem- onstrated that the effect of increased milking frequency on milk yield is more important in first parity cows than in older cows, others (Poole, 1982; DePeters et al. 1985; Bortacki et al. 2017) showed that multiparous cows respond better to frequent milking than primiparous cows, whereas The objective of this study was to investigate the effect of milking frequency (two times daily vs. three times daily) on the 305-d lactation milk, fat and protein yield and fat and protein percentage of Holstein dairy cows in Morocco. Data analyzed were 31400 records collected between 2009 and 2016 on 14272 cows raised in 194 herds. The frequency of milking had significant effects (P<0.05) on 305-d milk, fat and protein yield as well as fat percentage. The milk, fat and protein yield and fat percentage were higher by 265.1 kg, 13.3 kg, 5.8 kg, and 0.3 g/kg, respectively, i.e. 3,79%, 4.78%, 2.40%, and 0.75%, respectively, for cows milked thrice than those milked twice daily. However, the frequency of milking did not influence protein percentage (P>0.05). The interaction between parity and milking frequency was not significant (P>0.05) for any studied trait. Based on the results of this study, it can be concluded that increasing milking frequency increased milk, fat and protein yield as well as fat percentage regardless of parity. However, the additional milk yield obtained might not compensate for the cost of the labor generated by the extra milk- ing. KEY WORDS dairy cows, milk yield, milk composition, milking frequency, parity and milking frequency interaction. I. Boujenane 1* 1 Department of Animal Production and Biotechnology, Hassan II Agronomy and Veterinary Medicine Institute, Madinate Al Irfane, 10 101, Rabat, Morocco Received on: 24 Apr 2018 Revised on: 4 Aug 2018 Accepted on: 15 Aug 2018 Online Published on: Mar 2019 *Correspondence E‐mail: i.boujenane@iav.ac.ma © 2010 Copyright by Islamic Azad Univer ty, Rasht Branch, Rasht, Iran si Online version is available on: www.ijas.ir Research Article