Niacin supplementation improves growth performance and nutrient utilisation in Chinese Jinjiang cattle

Abstract In the present study, the effect of niacin supplementation on the growth performance and nutrient utilisation in Chinese Jinjiang cattle was investigated. A total of 48 finishing male Jinjiang cattle aged 24–30 months, with body weights of 200 ± 15 kg, were randomly divided into four groups. The cattle were fed a finishing diet (concentrate to forage ratio of 80:20). The diets for the control, NA320, NA480 and NA640 groups were supplemented with 0, 320, 480 or 640 mg/kg of niacin, respectively. The body weight and feed consumption of the 48 cattle were recorded on days 1, 28, and 56 of the experiment. Assessment of feed digestibility was conducted from days 52 to 56 of the study. Blood samples were collected from each animal on day 56. From days 1 to 56 of the study, the results indicated a significant increase in the average daily weight gains (p < .05) and lower feed to gain ratios (p < .05) for the NA480 and NA640 groups than for the control group. Furthermore, supplementation with 640 mg/kg niacin increased the apparent digestibility of all nutrients (p < .05), whereas supplementation with 480 mg/kg niacin enhanced the apparent digestibility of crude protein (p < .05). Moreover, supplementation with 480 and 640 mg/kg niacin increased the content of serum nonesterified fatty acids (p < .05). Therefore, it was concluded that supplementation with 640 mg/kg niacin in a high-concentrate diet may be beneficial to growth and nutrient utilisation in Chinese Jinjiang cattle.


Introduction
Jinjiang cattle, a breed indigenous to China, are revered for their great tolerance to roughage, excellent resistance to heat stress and desirable meat quality (China National Commission of Animal Genetic Resources 2011; Wu et al. 2011). Recently, several finishing trials were conducted to assess the viability of this breed for beef production (Bao 2015;Huang 2015). The productivity and meat quality of indigenous beef cattle can be improved through fattening using a high-energy, cereal-based concentrate (Priyanto et al. 2015). However, this diet can increase the risk of digestive diseases, such as ruminal acidosis, whereby the fermentable carbohydrate supply increases abruptly (Moya et al. 2009).
The vitamin niacin plays an important role in the metabolism of carbohydrates, lipids and amino acids. It has been reported that niacin produced by ruminal microbes alone may be insufficient to meet the requirements of high producing cattle (Flachowsky 1993). However, dietary supplementation with niacin can promote rumen fermentation, enhance the synthesis of ruminal microbial protein, increase blood T 3 and T 4 concentrations, increase nutrient digestibility, and improve the production performance in cattle (Flachowsky 1993;Girard 1998). Previously, we demonstrated that supplementation with 640 mg/kg niacin (approximately 6 g/day) in a high-concentrate diet inhibits the proliferation of Streptococcus bovis (in vitro assays) , regulates ruminal lactic acid metabolism, and stabilises ruminal pH in vitro . Furthermore, supplementation with 480 $ 640 mg/kg niacin in the high-concentrate diet improved the production performance in finishing Simmental cross bulls . In this study, we further explored the effect of niacin dietary supplementation on growth performance, nutrient digestibility and serum biochemical parameters in finishing Jinjiang cattle.

Materials and methods
This study was approved by the Animal Care and Use Committee of the College of Animal Science and Technology of Jiangxi Agricultural University.

Experimental design, animals and diets
A total of 48 finishing male Jinjiang cattle, aged 24-30 months, with body weights of 200 ± 15 kg, were randomly divided into four groups, with three replications and four cattle in each replication. The cattle were purchased from the National Original Breeding Farm of Jinjiang Cattle, Gaoan County, Jiangxi Province, China. The animals were provided a basal finishing diet (a high-concentrate diet, with a concentrate to forage ratio of 80:20) to meet the nutrient requirements for a daily gain of 500 g, based on the Chinese Feeding Standard for Beef Cattle (2004). The composition and nutrient levels of the basal diet are provided in Table 1. Animals in the control group were fed a basal finishing diet without niacin supplementation. Animals in the NA 320 , NA 480 and NA 640 groups were fed the same basal finishing diets but received a supplement of 320, 480 or 640 mg/kg of niacin, respectively. The niacin supplement provided to the animals in the present study was rumen-unprotected (purity !97%), (Nantong Repair-air Chemistry Bioengineering Co., Ltd.).
All animals were housed in fattening pens throughout the study period. During the trial, the cattle were tethered in a well-ventilated shed with individual feeding and watering arrangements. Prior to the start of the experiment, the animals were acclimated to the experimental condition for 15 days and fed a diet consisting of a concentrate to forage ratio of 20:80 (80% elephant grass, 15% corn, 2% soybean meal, 2% cottonseed, 0.5% limestone and 0.5% NaCl, DM basis). The experiment was conducted over a period of 56 days. During the test period, the cattle were fed a finishing diet, with a concentrate to forage ratio of 80:20. Feed was provided twice daily. The animals had free access to water. The feed amount was increased with the body weight of the animals, as determined using the following formula ( where TDMI ¼ total dry matter intake and LW ¼ live weight. One individual from each replicate group was selected for digestibility analysis from days 52 to 56 of the experiment. Faeces were collected thrice daily at 6:30, 15:30 and 22:30. A 10% sample was collected after weighting at each time point and then stored at 0-4 C. At the end of the digestibility trial, all faecal samples of each animal were combined and homogenised to create a single sub-sample for each animal. A total of 200 g of each homogenised sub-sample was freeze-dried and ground for further chemical analysis. To determine the feed intake, the amounts of forage and concentrate and the residual quantity were recorded daily for each animal. The forage samples were collected on days 1, 3 and 5 during the digestibility trial period. All forage samples were pooled over the 5 days of collection and dried at 60 C for 24 hours. Samples of the concentrate were collected on day 5 of the digestibility trial. Blood samples were collected from the jugular vein of each animal before feeding and watering at 7:00 am on day 56 of trial. Blood samples were centrifuged (3000 r/min) at 4 C for 10 min. Serum was collected and stored at -20 C for further analysis.

Measurements
On days 1, 28 and 56, each animal was weighed in the morning prior to feeding. The feed intake was determined according to the above method. The observed weights were used to calculate the average daily gain (ADG, kg/d), total dry matter intake (TDMI, kg/d), and feed to gain (F/G) rate in the early (1-28 d), late (29-56 d) and overall trial periods (1-56 d).
Crude protein (CP) was determined using the Kjeldahl method (AOAC 1984). Calcium (Ca) was estimated using the titrimetric method (AOAC 1990), and phosphorus (P) was determined by the colorimetric method (Donald et al. 1956). After the dried feed and faecal samples were ground, the dry matter (DM) and organic matter (OM) contents were analysed as previously described by Baur and Ensminger (1977). The neutral detergent fibre (NDF) and acid detergent fibre (ADF) content were analysed as previously reported by Van Soest et al. (1991). The apparent digestibility of nutrients with total faeces collection was estimated according to the following formula: Serum biochemical parameters, serum glucose (Glu), total protein (TP), urea nitrogen (UN), triglyceride (TG), total cholesterol (TC), non-esterified fatty acids (NEFA) and b-hydroxy butyric acid (b-HBA) concentrations, were determined using a Japan 7160 automatic biochemical analyser (Hitachi, Tokyo, Japan) in conjunction with a commercial kit (BioSino Bio-Technology & Science, Beijing, China).

Statistical analysis
Data were analysed with Statistical Package for the Social Sciences (SPSS 17.0, Chicago, IL) using a oneway analysis of variance (ANOVA). Duncan's multiple comparison test was used to compare significant differences between treatments. Values of p < .05 were considered significant. The results are presented as the means and pooled standard error of the mean (SEM).

Effect of niacin supplementation on cattle growth performance
The data collected on growth performance are presented in Table 2. The data illustrate that niacin supplementation did not exert a significant effect on the BW and TDMI of all groups over the total trial period. During the initial period (days 1 to 28), the ADG of the NA 640 group was significantly (p < .05) higher than in the control group, with an increase of 43.75%. Compared with the control group, NA 480 and NA 320 groups showed increases of 39.58% and 8.33%, respectively, in the ADG, although these differences were not statistically significant. With respect to the F/ G, the NA 480 and NA 640 groups showed a significant (p < .05) decrease by 26.07% and 31.61%, respectively, compared to that of the control group. Over the late period (days 29 to 56), there were no significant differences in the ADG among the groups. A significant decrease in the F/G (p < .05) was observed, decreasing by 20.10% and 25.78% in the NA 480 and NA 640 groups, respectively, compared to that of the control group. During days 1 to 56, the NA 480 and NA 640 groups showed significant (p < .05) increases (31.25% and 37.5%, respectively) in the ADG compared to that of the control group. Moreover, compared to the control group, the NA 480 and NA 640 groups showed significant F/G decreases (p < .05) of 23.34% and 28.88%, respectively.

Effect of niacin supplementation on digestibility of nutrients
Relative to the control group, the NA 640 group had 5.99%, 4.76%, 6.87%, 6.99% and 22.24% increases (p < .05) in the digestibility of DM, OM, CP, NDF and ADF, respectively. Only the NA 480 group exhibited a significant (p < .05) difference in the apparent digestibility of CP compared with that of the control group. There were no significant differences in the apparent digestibility of all nutrients between the NA 320 group and the control group. Therefore, supplementation with 640 mg/kg niacin made the greatest improvement in the apparent digestibility of dietary nutrients among all treatment groups tested (Table 3).

Effect of niacin supplementation on serum biochemical parameters
The serum biochemical parameters of finishing Jinjiang cattle are presented in Table 4. The concentration of serum NEFA increased significantly with increasing niacin dosage. However, there were no significant differences in serum NEFA between the NA 320 and control groups. In contrast, the serum NEFA levels of the NA 480 and NA 640 groups were 2.95-fold and 4.20-fold greater, respectively, than the levels in the control group (p < .05). The serum NEFA level of NA 640 group was 1.42-fold greater than that of the NA 480 group (p < .05). There were no significant differences in the serum levels of GLU, TP, UN, TG, TC or b-HBA among all groups. Therefore, the supplementation with niacin appeared to only improve the serum NEFA levels in Chinese Jinjiang cattle.

Growth performance
When the feed provided to feedlot cattle is altered from a high-forage to a high-concentrate diet, marked changes in the ruminal environment often result (Bevans et al. 2005). Consequently, the cattle may suffer from conditions such as ruminal acidosis, damage to the ruminal mucosa, dehydration and even metabolic acidosis (Moya et al. 2009;Laskoski et al. 2014). Ouyang et al. (2014) reported that supplemented niacin can regulate ruminal lactic acid metabolism, promote rumen fermentation and stabilise the ruminal environment. Niacin supplementation has been demonstrated to have a positive effect on cattle growth performance (Horton 1992;Srinivasan et al. 2004;Kumar and Dass 2006). In this study, dietary supplementation with 480-640 mg/kg of niacin was shown to improve growth performance in Jinjiang cattle, whereas a daily dose of 320 mg/kg of niacin did not have a significant effect on ADG and F/G. This suggests that niacin probably plays an important role in the growth performance of Jinjiang cattle in a dosedependent manner. It has been reported that low doses of niacin (100-400 ppm) did not improve animal growth performance, probably due to its breakdown in the rumen by ruminal microbes (Zinn et al. 1987). Recent studies have focussed on the application of rumen-protected niacin to cattle. Yuan et al. (2012) reported that rumen-protected niacin was not degraded in the rumen, but was degraded and absorbed in the small intestines, allowing for the positive effects to be exerted in the small intestines. We have observed that supplementation with niacin exerted more beneficial effects during the early period in comparison with the late period. This effect could be a result of the adaptation of animal and ruminal microbes to high-concentrate diets, along with the compensatory growth of the cattle. Chang et al. (1995) reported that niacin supplementation increased live weight gain in calves only during periods of stress but not during periods of normal growth. The efficacy of supplementation during times of stress could be a result of the niacin supply possibly being deficient during periods of elevated stress due to the reduction of DMI and microbial niacin synthesis in the rumen (Schwab et al. 2005).

Digestibility of nutrients
It has been previously reported that there were no significant differences in nutrient digestibility between the cattle fed diets supplemented with niacin and those fed non-supplemented diets (Kumar and Dass 2006;Doreau and Ottou 1996;Campbell et al. 1994). However, Horner et al. (1988) reported increased digestibility of both the CP and NDF in mature, nonlactating Holstein heifers fed a diet supplemented with 0.07% niacin (6 g niacin/9.1 kg DM consumed). This effect may have been due to the growth of ruminal microbes resulting from niacin supplementation. In the present study, nutrient digestibility was increased in a dose-dependent manner with niacin supplementation in finishing Jinjiang cattle. One plausible explanation for this result could be interpreted as alterations in the ruminal microbial population resulting from the change in niacin levels Kumar and Dass 2005;Samanta et al. 2000) when the composition of the feed ratio was shifted from a highforage to a high-concentrate diet.

Blood biochemical parameters
The effect of niacin on blood biochemical parameters has been studied extensively in dairy cattle (Niehoff et al. 2009). Kumar and Dass (2006) reported that there was no significant difference in the concentrations of serum GLU, TP, UN, TG and TC in response to niacin supplementation. In contrast, Ghorbani et al. (2008) reported that the concentration of serum GLU increased, whereas the concentration of TG and TP decreased in dairy cows when diets were supplemented with niacin during the early lactation period. El- Barody et al. (2001) supplemented feed with either 6 or 12 g niacin/head per day and reported a decrease in serum TC concentration in pregnant Egyptian buffaloes. This observation was in agreement with the findings of a study published by Kumar and Dass (2006) in male buffalo calves. These findings can be attributed to the marked inhibition of fat utilisation by niacin (Waterman et al. 1972). Our results revealed that supplementation with niacin had no effect on serum GLU, TP, UN, TG and TC content, but supplementation significantly increased serum NEFA. These observations are consistent with the findings of Martinez et al. (1991) and Drackley et al. (1998). This could be explained by assuming that niacin stimulates lipoprotein lipase activity (Nelson et al. 2012) in finishing cattle to improve energy supply. During early lactation, high-producing cows are physiologically in a state of negative energy balance (Grummer 1993). These animals may suffer from ketosis resulting from lipid metabolism disorders, and the increase of serum b-HBA is observed as well during this period (Bobe et al. 2004). Experimentally, niacin has been shown to exert antilipolytic effects, resulting in an immediate reduction in serum NEFA and b-HBA (Morey et al. 2011). Yuan et al. (2012) reported more positive effects of rumen-protected niacin on the decrease of serum NEFA and b-HBA, resulting from the effective modification of lipid metabolism. In the present study, no significant effect of niacin supplementation on serum b-HBA was observed. This may be due to the low concentrations of serum b-HBA in cattle fed with a highconcentrate diet, so the effect of niacin was minimal.

Conclusions
In the present study, dietary supplementation with 480 À 640 mg/kg of niacin significantly increased ADG while decreasing F/G in finishing Jinjiang cattle. Niacin supplementation significantly increased serum NEFA levels. Furthermore, supplementation with 640 mg/kg niacin significantly increased the apparent digestibility of nutrients, and 480 mg/kg of niacin increased the digestibility of CP in finishing Jinjiang cattle. Taken together, it can be reasonably concluded that the addition of 640 mg/kg niacin to a high-concentrate diet could increase the growth performance and nutrient utilisation efficiency in finishing Jinjiang cattle.

Ethical approval
This study was approved by the Animal Care and Use Committee of the College of Animal Science and Technology of Jiangxi Agricultural University.

Disclosure statement
No potential conflict of interest was reported by the authors.