ANIMAL SCIENCE

Cutting age and nutritional value of mulberry (Morus alba) foliage meal for pigs

S. Mireles^{1  *}  , E, Moreno¹  , M. Ruiz¹  , Pok Samkol²  , Y. Caro³  , D. González⁴  , J. Ly^1,2,3 

¹Centro Universitario de Ciencias Biológicas y Agropecuarias (CUCBA), Universidad de Guadalajara, Zapopan, Jalisco, México

²Fundación para la Universidad de Agricultura Tropical. Real Universidad de Agricultura. Chamcar Daung, Phnom Penh, Camboya

³Instituto de Ciencia Animal, Apartado 24, San José de las Lajas, Mayabeque, Cuba

⁴Facultad de Agronomía, Universidad Central de Venezuela. El Limón, Maracay, Venezuela

ABSTRACT

Twelve plots of 15 m² planted with an indeterminate variety of mulberry (Morus alba) with wide leaves underwent periodic cuts every 30, 60, 90 and 120 days to study, according to a random block design, the nutritional value of mulberry foliage meal by the technique of in vitro ileal (pepsin/pancreatin) and fecal digestibility. Cell wall content and N bound to that wall increased significantly (P = 0.004) with the cut age while the N content tended to decrease (P = 0.059). The ileal digestibility of organic matter and N decreased from 68.1 and 59.4% to 44.2 and 30.0% (P <0.05), respectively, in samples of 30 cutting days up to others of 120 days (P <0.01). Similarly, fecal digestibility of DM and organic matter went from 66.7 and 68.0% to 45.3 and 51.0% (P <0.01), respectively. Cutting age exerts a determining influence on the nutritional value of mulberry foliage meal provided to pigs, which worsens as cut frequency decreases.

Key words: tree forage; pigs; digestibility; yield; fiber

INTRODUCTION

The use of tree foliage, in general, and mulberry in the feeding of pigs and other animals of zootechnical interest has been reviewed in recent years (^{Ly 2004}, ^{Martin et al. 2007}, and ^{Ly and Samkol 2014}). Other studies, especially concerning the use of legume foliages in pig feeding, have also been of interest for researchers in the Latin American tropics (^{Martens et al. 2012}), or for non-legume foliages and fiber materials, in Indochina (^{Phiny 2012} and ^{Tran 2012}).

There is no available precise information on the influence of mulberry cut age on indicators of economic importance such as performance and digestibility traits of diets with mulberry, provided to pigs (^{Martín et al. 2007}), but it is known that young leaves are more nutritional than the old ones in pigs (^{Samkol et al. 2005}). It is known that, in other livestock species, this is a factor of considerable importance (^{Boschini 2001}, ^{Noda et al. 2011} and ^{Avila et al. 2012}).

The objective of this paper was to inform about the effect of the cutting age of mulberry tree foliage, in its nutritional value for pigs. In the knowledge of the authors, there is no history of this type of research in pigs fed mulberry foliage.

MATERIALS AND METHODS

Twelve plots of 15 m² (3x5 m) planted with an indeterminate variety of mulberry (Morus alba) with wide leaves, after initial sowing (distance, 0.5 m) and to which an initial even cut was made six months after sowing, were subjected to periodic cuts every 30, 60, 90 and 120 days to study the nutritional value of mulberry foliage meal by the in vitro technique of ileal (pepsin/pancreatin) and fecal digestibility. Mulberry was planted with cuttings of about 20 cm, and periodically fertilized with effluent from digesters loaded with porcine excreta (100 kg N / ha per year), in an integrated animal production system. The sample taken at random in each plot came from the central rows to avoid the border effect, and it was representative of the foliage of the second periodic cut, when the whole plot was harvested. The cutting height was constant and equal to 30 cm maximum.

Mulberry foliage was devoid of the central stems, to obtain a material that mostly contained leaves and petioles, as well as stems no more than 3 mm in diameter. In a representative fresh sample of each plot, DM content was determined by drying in a microwave oven (^{Undersander et al. 1993}). The material was spread on sheets of black polyethylene on the ground in order to be dried under the sun, for three days, and then converted into foliage meal, when ground in a hammer mill with a sieve size of 1 mm. Representative samples of the foliage meal were taken, corresponding to three per each cutting age, and the content of residual DM, ashes, crude fiber and N were determined by recognized procedures (^{AOAC 2006}) in aliquots of the samples. The technique of dissolution in detergent solution was used for determining the NDF concentration (^{Van Soest et al. 1991}). The organic matter was calculated as the difference between 100 and ash percentage. The N linked to the NDF was determined according to ^{Licitra et al. (1996)}. The wash value or water solubility of DM and N was carried out by the procedure suggested by ^{Ly and Preston (2001)}.

The determination of in vitro digestibility simulating the ileal was carried out according to the method of ^{Dierick et al. (1985)}, with the use of casein as a pattern substance. For in vitro fecal digestibility, ^{Löwgreen (1992)} procedure was followed and porcine fecal material recently excreted by adult pigs was used, and wood cellulose as a pattern substance. All determinations were conducted in quadruplicate. A random block design was applied for numerical manipulation. Thus there were three blocks per treatment, and the treatment was the cut age. Means were processed according to the analysis of variance technique (^{Steel et al. 1997}). When this analysis detected significant differences (P <0.05), the means were compared by Duncan multiple comparison test. The interdependence among some chemical-physical characteristics of the studied foliage and its ileal digestibility, in vitro, was established by means of a Pearson correlation matrix (^{Steel et al. 1997}). When it was considered convenient, regression analysis was also carried out. Data processing was performed through a statistical package (^{Minitab 2009}).

RESULTS AND DISCUSSION

Table 1 shows the mulberry foliage yield.

Tabla 1 Anual yield of mulberry foliage in this experiment 

	Cut age, days				SE ±	P
	30	60	90	120
n	3	3	3	3	-	-
Fresh foliage, t/ha	15.52^a	17.41^a	34.22^b	38.46^c	2.93	0.001
Dry foliage, t/ha	3.88^a	5.03^a	10.43^b	12.90^c	0.42	0.001
Dry matter, %	25.06^a	28.90^ab	30.53^b	31.10^b	1.41	0.006

¹branches cut at 30 cm from the soil

^abcdMeans without common letters in the same row differ significantly among them (P<0.05)

Even with a lot of variability, fresh foliage yield was higher while the cutting frequency was lower (P = 0.001). Also the annual yield of dry foliage increased significantly (P = 0.001), in this case, from 3.88 to 12.90 t DM/year when the cut age went from 30 to 120 days. On the other hand, it was noted that DM concentration in the foliage increased significantly (P = 0.006) from 25.06 to 31.10% depending on the cut of foliage from 30 to 120 days, the increase in the yield of mulberry with the decrease of cutting frequency has been previously reported (^{Boschini 2001}, ^{García Soldevilla and Fernández 2004} and ^{Noda et al. 2011}), and this experiment would confirm these other observations.

Table 2 shows the effect of cut age on chemical composition of mulberry foliage.

Tabla 2 Effect of cut age on chemical composition of mulberry foliage meal¹ (percentage under dry basis) 

	Cut age, days				SE ±	P
	30	60	90	120
n	3	3	3	3	-	-
Ashes	7.50^a	8.00^a	13.07^b	16.62^c	0.59	0.001
Organic matter	92.50^a	92.00^a	86.93^b	83.38^c	0.59	0.001
Crude fiber	8.63^a	10.06^a	17.43^b	19.73^b	1.73	0.001
NDF	24.33^a	26.70^a	28.43^ab	32.73^b	1.50	0.004
N	5.02	5.01	4.25	3.61	0.33	0.059
NDF-N	1.32^a	1.40^a	1.72^ab	1.92^b	0.17	0.004
NDF-N, % total N	29.77^a	28.03^a	41.16^b	49.70^b	3.44	0.001
Soluble DM	44.83^a	39.03^b	31.33^c	25.33^d	1.91	0.001
Soluble N	48.13^a	42.30^a	33.93^b	24.33^c	1.60	0.001

¹Branches cut at 30 cm from the soil

^abcdMeans without common letters in the same row differ significantly among them (P<0.05)

When the cut age went from 30 to 120 days, cell wall content (NDF, P = 0.004) and N content bound to that wall increased (NDF-N, P = 0.004). Likewise, the percentage of crude fiber increased (P = 0.001), and, at the same time, solubility values of MS and N decreased (P=0.001). These data, which are obvious signs of foliage senescence, are consistent with those of other researches in which the same evolution of tree foliage with aging has been found (^{Boschini 2001}, ^{Samkol et al. 2005}, ^{Noda et al. 2011} and ^{Avila et al. 2012}). Obviously, a higher content of N bound to the wall implies a lower availability of amino acids for the animal during digestive processes that take place in the pig (^{Ly 2008}).

The effect of cut age on in vitro ileal digestibility is presented in table 3. Ileal digestibility of organic matter and N decreased from 68.17 and 59.46% to 44.37 and 30.00% (P = 0.001) in 30-day-cut samples of until 120 days. Data found in this experiment with pigs confirm previous ones (^{Samkol et al. 2005}) and show the same inclination as those results of ^{Boschini (2001)} with in situ degraded mulberry, in the rumen.

Table 3 In vitro ileal digestibility (pepsin/pancreatin) of mulberry foliage meal ¹ (percentage under dry basis) 

	Cut age, days				SE ±	P
	30	60	90	120
n	3	3	3	3	-	-
Dry matter	63.13^a	54.96^b	43.20^c	35.56^c	2.75	0.001
Organic matter	68.17^a	60.70^ab	52.76^b	44.37^c	4.15	0.002
N	59.46^a	52.23^b	41.87^c	30.00^d	1.95	0.001

¹Branches cut at 30 cm from the soil

^abcdMeans without common letters in the same row differ significantly among them (P<0.05)

Some apparent relations of cause/effect among in vitro digestibility indexes and other physical and chemical of foliage appear in the matrix of correlation of Pearson of table 4.

Table 4 Association of in vitro digestibility (pepsin/pancreatin) of mulberry foliage with other physical and chemical characteristics of samples (n = 12) 

	MSS1	NS	DMD	ND	NDF	NDF -N
NS	0.981
DMD	0.992	0.974
ND	0.985	0.993	0.980
NDF	-0.842	-0.880	-0.838	-0.884
NDF-N	-0.869	-0.853	-0.855	-0.863	0.704
CF	-0.889	-0.880	-0.882	-0.900	0.777	0.910

¹MSS and NS express the washing of DM and N; DMD and ND express in vitro digestibility (pepsin/pancreatin); NDF, NDF -N and CF express the content of NDF, NDF -N and crude fiber in the foliage. All measures are expressed in percentage P<0.05 for r>0.6.

Figure 1 shows the interdependence found between in vitro digestibility of N (pepsin/pancreatin) of N and N content bound to the plant wall (P = 0.001). It was positive to find such a response even with a relatively small population size. The decrease in the values of in vitro digestibility of N with the increase of the N content linked to the plant wall, support the perception that with the increase in the age of cut, the nutritional value of mulberry foliage decreases, which it had been suggested by ^{Samkol et al. (2005)} when they examined this interdependence in samples of tropical trees and shrubs.

Figure 1 Relationship between in vitro digestibility of N (pepsin/pancreatin) and N bound to the wall of mulberry foliage (Syx, ± 6.28) 

The effect of cut age on in vitro fecal digestibility is shown in table 5. Rates of rectal digestibility were obviously higher than those observed for ileal digestibility, because, in this case, they include digestive processes that take place in the caecum and colon (^{Ly 2008}). As the age of cut was higher, the difference between fecal and ileal in vitro digestibility increased, for DM and for organic matter. As an illustration, in the case of N, 0.04% disappeared in the large intestine when the cut was made every 30 days, while at 120 days, the disappearance in that same segment of the food canal, amounted to 21.13%. These data are inclined to support the hypothesis that foliage aging modifies the digestion strategy of pigs, with a greater participation of indigenous microflora, to take advantage of nutrients contained in old mulberry. Even so, the microbial attack on the available substrates may be done with greater difficulty. In studies of ruminal digestibility of mulberry forage, ^{Boschini (2001)} found an equivalent pattern, with mulberry trees with a regrowth age between 56 and 112 days.

Table 5 In vitro fecal digestibility of mulberry foliage meal¹ (percentage under dry basis) 

	Cut age, days				SE ±	P
	30	60	90	120
n	3	3	3	3	-	-
Dry matter	66.77^a	58.40^ab	50.13^bc	45.37^c	4.01	0.001
Organic matter	68.07^a	63.10^ab	52.27^bc	48.90^c	5.22	0.013
N	59.50^a	58.33^a	57.63^ab	51.13^b	2.97	0.050

¹Branches cut at 30 cm from the soil

^abcdMeans without common letters in the same row differ significantly among them (P<0.05)

In this test, in vitro fecal digestibility of DM decreased from 66.77 to 45.37% (P = 0.001) while the organic matter declined from 68.07 to 48.90% (P = 0.013). In contrast, nitrogen fraction of samples showed little significant influence (P = 0.050) due to treatment effect. These results of in vitro ileal and fecal digestibility of mulberry foliage, mostly agree with others in which the effect of cutting age or foliage aging influence significantly on the decrease of their digestive indexes (^{Noda et al. 2011}, ^{Avila et al. 2012} and ^{Ly et al. 2018}).

According to the results of this research, the cut age exerts a determining influence on the nutritional value of the mulberry foliage meal provided to pigs. Factors such as fertilization level and cultivated variety of mulberry may interact with the cut age. Other strategies to consider could be the feeding of growing pigs or breeding sows with mulberry foliage meal, and levels of inclusion in the diet.

ACKNOWLEDGEMENTS

Thanks to the laboratory work performed at the Foundation of the Universidad de Agricultura Tropical, Chamcar Daung. Thanks to the staff of the pig farm of the Facultad de Agronomía, Universidad Central de Venezuela, in Maracay, for the technical support for the development of this experiment. Finally, thanks are given to Dr. Marisol Muñiz, Instituto de Investigaciones Porcinas, Punta Brava, for her suggestions about the design and biometric manipulation of data.

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Received: January 04, 2018; Accepted: July 03, 2019

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