Milk composition is the result of various biological reactions, affected by feed intake and physiological status of animal. Physiological status, in turn, is affected by environment modulated through hypothalamus and pituitary. Milk composition and quality are important characteristics that determine the nutritive value and consumer acceptability. The following three studies were conducted to investigate relationship of lactation stage and body condition with milk yield and composition with special reference to fatty acids in crossbred dairy cows and buffaloes (Bubalus bubalis) under tropical conditions. Study I - Variation in milk fatty acids composition with body condition: A total of 24 Nili-Ravi buffaloes within 60 days after parturition, were selected from a private dairy farm at district Peshawar. All the animals consumed the same diet during the experimental period. A total of 576 raw milk samples were collected for laboratory analysis. The study continued up to 6 months during the year 2008. Body condition score (BCS), milk yield and composition were recorded once a week. Means for milk fatty acids profile were compared for various levels of BCS. The mean milk yield and fat contents were 9.28 kg/d and 5.36 %, respectively. The total saturated fatty acids (SFAs) were 64.22 g/100g of total fatty acids and the unsaturated fatty acids (UFAs) were 35.79 g/100g of total fatty acids. Out of the SFAs, highest amount was recorded for C16:0, followed by C18:0 and C14:0. The total sum of hypercholestrolemic fatty acids (HCFAs, C12:0, C14:0 and C16:0) were 43.33 g/100g of total fatty acids. The concentrations of UFAs were greater with the moderate (2.5) BCS followed by poor (1.5) and highest one (3.5) while the SFAs showed an opposite trend. The correlation analysis showed that milk yield was negatively affected by BCS and milk fat positively though, non-significantly. The present study suggests that Nili-Ravi dairy buffaloes produce milk, with the highest concentration of C18:1 cis-9. Two HCFAs (C12:0 and C14:0) were associated with higher body condition. Buffaloes with moderate body condition yielded milk containing healthier fatty acids. Study II - Changes in milk fatty acid profile with advancing lactation: This study was conducted to determine the effect of lactation advancement on milk yield and its fatty acid composition in crossbred cows during the initial 16 weeks of lactation. A total of 28 F1 crossbred cows (HF x Sahiwal) within 1st week after parturition were selected from a large state farm. The animals were maintained under uniform management conditions in a well-ventilated shed. The animals were milked twice and milk samples were collected from each cow once a week during 1, 4, 8, 12 and 16 weeks of lactation. BCS and milk yield were recorded on the day of sample collection. Means for milk fatty acids composition were compared for five weeks (1, 4, 8, 12 and 16) of lactation. The i total amount of saturated fatty acids (SFAs) was on the average 67.88g/100g of total fatty acids and the unsaturated fatty acids (UFA) were 32.39 g/100g of total fatty acids. In the SFAs the highest amount was of palmitic acid (23.09 g/100g of total fatty acids). The highest monounsaturated fatty acids (MUFAs) level was of oleic acid (C18:1 cis-9, 24.68 g/100g of total fatty acids). Mean concentration of polyunsaturated fatty acids (PUFAs) was 3.95 g/100g of total fatty acids. The total sum of medium chain fatty acids C12:0, C14:0 and C16:0 identified as hypercholestrolemic fatty acids (HCFAs) was 38.40 g/100g of total fatty acids. The correlation analysis showed a significantly positive relationship between BCS and milk fat percent. The present study suggests that concentrations of UFAs were higher in earlier weeks and declined during mid lactation. With advancement of lactation, from wk 1 to 16 of lactation, the proportion of both de novo fatty acids and PUFAs increased and pre-formed fatty acids (specifically C18:0 and C18:1 cis9) decreased. The two hypercholestolemic fatty acids (C12:0 and C14:0) increased with advancing lactation and the cows in early lactation yielded milk containing healthier fatty acids. Study III - Body condition score as an indicator of milk yield and composition: This study was undertaken to evaluate the role of body condition score (BCS) as an indicator of milk yield and composition in Nili-Ravi buffaloes under subtropical conditions. A total of 36 buffaloes within 1st week of parturition were selected from a private peri-urban dairy farm at district Peshawar. All the animals were offered green fodders ad libitum and concentrate at the rate of 1kg per 2 kg of milk produced. Milk yield (kg/d) and BCS (scale 1-5) were recorded weekly and milk samples (n = 1008) were collected for analysis of fat, protein and lactose contents. The study continued for 7 months, starting from November 2007 to May 2008. BCS significantly affected milk yield and fat and protein contents. Lactose was least affected with changes in BCS during lactation. Highest yield was recorded with moderate BCS in buffaloes. BCS correlated positively with milk fat and protein and negatively with milk yield. Milk yield decreased while BCS increased with advancing lactation. The negative relationship may be due to mobilization of body reserves, indicating better genetic potential of buffalo as a dairy breed. The results indicated that BCS may be used as an indicator for maintaining milk yield and composition in dairy buffaloes. Keywords: Dairy buffalo, crossbred cows, milk composition, milk yield, lactation stage, body condition score, saturated fatty acids, unsaturated fatty acids, hypercholestrolemic fatty acids