Modeling growth curves to estimate the suitable slaughter age for the Vietnamese Tap Na pig

•The best model to describe the growth of Tap Na castrated males was Gompertz.•The best model to describe the growth of Tap Na females was Richards.•Maximum monthly gain for Tap Na pigs was 6 months (castrated males) and 7 months (females).•The suitable slaughter age was 8.84 months for Tap Na castrated males (82.99 kg).•The suitable slaughter age was 10.60 months for Tap Na females (95.25 kg). Tap Na is an indigenous pig breed which plays an essential role in livestock development in the mountainous Cao Bang province, Vietnam. This study aimed to find the best model to describe the growth of Tap Na pigs, and then predict the live weight, weight gain, and suitable slaughter age by using the best growth model. The body weights of 100 pigs (50 castrated males and 50 females) were measured every month from birth to 10 months of age. The data for growth performance were analyzed in R using eight mathematical functions (von Bertalanffy, Bridges, Janoschek, Gompertz, Logistic, Lopez, Richards, and Weibull). The best models to describe the growth of Tap Na castrated males and females were Gompertz and Richards, respectively. The upper asymptotic body weights (α) were estimated to be 96.00 kg (Logistic) to 192.66 kg (von Bertalanffy) for castrated males, whereas these α values for females were from 102.42 kg (Logistic) to 167.82 kg (von Bertalanffy). The predicted ages at the beginning of the growth acceleration phase were different between castrated males (2.25 to 2.85 months) and females (2.29 to 3.39 months). Consequently, the inflection points and estimated ages at the end of the growth deceleration phase were also different between castrated males and females. The maximum absolute growth rate (monthly gains) occurred at 6 months of age for castrated males and 7 months for females. The maximum average monthly gains were recorded at 8.84 and 10.60 months of age for castrated males and females, respectively. This suggested the suitable slaughter ages are 8.84 months for Tap Na castrated males (82.99 kg) and 10.60 months for females (95.25 kg).